Volts, amperes and watts: which power supply unit for which device?

You also have a box full of power supplies and don't know which one goes with which? It doesn't really matter, basically you can take any, as long as the volts and amps are right: Volt, i.e. the voltage must match the device and power supply unit; if the power pack delivers too much voltage, the device (tends to) break down, if it delivers too little, the device doesn't work. at Ampere However, this is a maximum specification: If the device requires more amps than the power supply unit can supply, it will not work and the power supply unit will break (unless it is fused). If the device requires fewer amps, the power adapter is simply not fully utilized.

power adapter
Volt must match the device, Ampere may be greater than the device.

The right power supply with the right voltage

A power supply with 5 volts and 1 amps can therefore be used for all devices that require 5 volts and 1 ampere or less (which is not to say that a device here and there is not particularly finicky and cannot, for example, cope with the voltage fluctuations of a non-original power supply). And if you multiply both, you get the power consumption in watts: A typical USB power supply (e.g. from a smartphone) with 5 V and 2 A has a maximum output of 10 watts.

And since such questions keep coming up, here they are again in brief:

  • Volt must fit exactly.
  • Ampere may be higher for the power supply.

Example: 5 amp, 12 volt power supply can power devices that exactly 12 volts and maximum 5 amps desire.

By the way: There is a handy Watts/Amps/Volts calculator here.

PS: A previous version of the article had different numbers, so some of the comments are no longer applicable - just for clarity.

PPS: Since the article has been very popular for 9 years now and has raised all kinds of questions, there is now a whole website based on it with much more information about volts, amps, watts and power supplies - have a look VoltAmpereWatt.de.

Addendum: Here are a few links to universal power supplies that might be useful:

First the variant for normal home use with 3 to 12 volts at 2 amps:

Product prices and availability are correct as of the date/time shown and are subject to change. All pricing and availability information on https://www.amazon.de/ at the time of purchase applies to the purchase of this product.

Something similar is also available for laptops:

Product prices and availability are correct as of the date/time shown and are subject to change. All pricing and availability information on https://www.amazon.de/ at the time of purchase applies to the purchase of this product.

And for the daring, of course, there's that, too really universal universal power supply – including the option to scrap everything that comes near it:

Product prices and availability are correct as of the date/time shown and are subject to change. All pricing and availability information on https://www.amazon.de/ at the time of purchase applies to the purchase of this product.

So serious: Be careful with universal power supplies! It cost me a camera many years ago because I had set 9 instead of 6 volts ...

Mirco Lang

Freelance journalist, Sauerland exile, (fairly old) skateboarder, graduate computer scientist, retail salesman, open source nerd, Checkmk handbook writer. Ex-Saturn'ler, Ex-Data-Becker'ler, Ex-BSI'ler. First contact with computers: ca. 1982 - a friend's big brother's C64. If you want to read more about open source, Linux and craft stuff and support Tutonaut here: About Coffee sponsorship via Paypal.I'm always happy. In advance: Thank you! Do not miss: cli.help and VoltAmpereWatt.de. New: Mastodon


  1. Hallo,

    I looked on the Internet but only found the wrong thing (wrong starting point).

    So I have a new cell phone...

    Xaomi Blabla –> 120 watts
    (Charges via a less flexible USB-A cable.)

    There is a power bank...
    (Power bank supports PD (Power Delivery) 3.0)
    Safeul Blabla –> 30 watt PD with USB-A output…..

    Can they communicate or is the cell phone stubborn and demanding 120 watts of power?

    Unfortunately I can't find anything on Xaomi or Safeul.

    Many many thanks!

    Greetings R. Lautenschläger

  2. Hello Mirco,
    Unfortunately, I also have an additional question. Similar to Harald Ege, I'm looking for a 12-volt DC connection. A truck battery with a solar panel is fed into the holiday home. The battery then provides power for lighting and charging smartphones. Now I have bought a projector with a battery, which has a power supply with an output of 12 volts 2A and is connected to the projector using USB C. However, the input power for the included power supply is 110V to 240 volts. So I can't use this. When looking for a car adapter, the output power is usually given as 5 volts. Are these 5 volts enough to charge the projector? Will it just take a little longer or will I ruin the projector?
    Link to the projector with all technical features. Declarations: https://toumeipro.com/products/c900-portable-smart-dlp-projector?variant=32906568204335
    Thank you very much for your answer!

  3. Hii, I see that there is apparently a capable electrician here and that he is always in demand.
    I have already written to Bosch, but they are waiting for an answer.
    I bought an 18 V garden pump, which includes a 2,5 AH all-in-one battery.
    Can this pump also be run for a long time with a 4 AH battery, or are you guessing
    rather off here.
    18V 3 600 HC 100, IPX8


    1. The ampere-hours only indicate the capacity - and that can basically be any size. As long as the battery supplies at least as many amps as required and exactly 18 volts, you can use the battery. Whether 2 or 4 or 12 ampere hours is irrelevant for correct operation.

      A probably more theoretical exception: If the battery is permanently installed and not to change is intended and also no wired operation provided, the consumer could of course be designed in such a way that he should not run longer at a time than the built-in battery allows - because otherwise he might get too hot. But it's a very far-fetched idea ;)

  4. Hello Mirco

    Thank you for your informative article.
    I'm still a little confused and have a quick question.
    Namely, I would like to operate a Peltier element, which has a maximum operating current of 15 A and a maximum operating voltage of 15.4 V, with approx. 11 V and approx. 10 A. I have a 435 watt Pc power pack at my disposal, which can deliver a current of up to 12 A with a 33 V output. May I now attach the Peltier element to this output without any worries?
    Otherwise, I thought about connecting a 12 V CPU water cooling system together with the Peltier element in parallel to the same 12 V output of the Pc power supply.
    Please correct me if I'm talking nonsense.
    I would be very happy about your help.
    Thank you again

    1. So I first had to see what a Peltier element actually is, so everything I say should be treated with caution ;)
      But yes, that should fit, the 12 volts are within the specifications and there is enough current available at 33 A, regardless of whether it is ultimately 10 amps or a little more - even at full load with 15,4 V * 15 A = 231 W, the power supply would hardly shrug its shoulders. And the Peltier element itself just draws the current it uses at 12V, so all good. (Only with 11 volts the thing will not be able to be operated via the 12 V output, I suspect a typo (or overlooked a control option)).

      You could certainly add water cooling, but that would not have an impact on the Peltier element. Unless you use it to cool the hot side...

      1. Thank you very much! You helped me a lot. I'll probably really add the water cooling because it's really meant for the warm side of the element.
        thank you again

  5. Hello Mirco,

    I still have a question about your basic article: You say the voltage must be right, the power or current may be too high. So far so good. But what about the difference between 12 V AC/DC and 12 V DC. AC/DC, as far as I know, is half-wave alternating current while DC is pure direct current. Do devices whose original power pack supplies 12 V AC/DC also work with pure 12 V DC?
    The background to the question: I own a mobile home that is relatively self-sufficient on the electricity side thanks to photovoltaics on the roof. Unfortunately there is no 230V inverter available. This means that 230V is only available when the mobile home is connected to shore power. However, I use some devices that are battery operated, but need 230V power supplies with 12V AC/DC output for charging. The idea was why not charge directly via the 12V vehicle electrical system? But that's DC!

    Thank you in advance for your reply.

    1. There is a bit of a problem in the details, AC/alternating current is alternating current, DC/direct current is direct current - the "AC/DC" on power supplies only means that the power supply takes AC and outputs DC, giving an "AC/DC output". it not. If the devices need 12 volts DC, they can also be connected directly to the 12 volt vehicle electrical system, for example with a simple one like this 9 euro DC cigarette lighter adapter. Something like that is also available as a universal power supply with several plugs and outputs, here for about 40 euros.

  6. Hello, Mr Lang.

    My question to you would be this:

    The power pack for charging a car starter power battery (i.e. the additional things that you can quickly connect to the battery, keyword: power bank) has certain volt-ampere values.

    After a few STARTING HELP/ATTEMPTS, you have to recharge these ADDITIONAL STARTING BATTERIES at the socket with the power pack.

    For this you need a power supply unit, a mains adapter or a power pack. (You can find different names for it.)

    The original power pack had (had) an "output" of 14 V 1 A ... according to the instructions for use and technical data from the manufacturer of the power bank. OUTPUT is apparently exactly the plug hole in the POWERBANK where you should put in/plug in the power supply.

    I QUOTE without naming a company:

    To load the POWER PACKAGE:
    1 x power plug (Input (AC): 100V / 240V / Output (DC): 14V / 1A)
    1 x car charger cable (Input/Output: 14V/1A (via cigarette lighter))<

    charging in the vehicle
    The POWER PACK can also be charged with the 12 V cigarette lighter charging cable.<

    Unfortunately, I lost this original power supply. Now I'm looking for a new (replacement) power supply with EXACTLY the output 14 V 1 A, but I can't find any.

    But I find (other) power supplies, e.g. B. for monitors. They have 14 V, okay, but then they have other A=AMPERE, e.g. 4A or 2,7A.

    My problem: Which network device could I use (at all)?

    I have to recharge the starter thing, but I also don't want to damage it.

    I can't use a power supply unit with an output of 12 V?

    Does it have to be exactly 14 V 1 A? SO 14 VOLTS and 1 AMP?

    Isn't there an alternative?

    I have a number of power supplies in the house, but they always have 12 volt OUTPUT. They would damage the POWERBANK device?

    well? What to do? If only EXACTLY 14 V 1 A is allowed, then I would probably have to call the manufacturer for the POWERBANK START ASSISTANCE. (And they will hardly sell a single power supply. They want to sell the POWERBANK as a complete offer, not just the power supply.)

    Best regards and many thanks, Klaus Jans (Even the smallest things in life seem to be highly complex!)

    1. So the 14 volts should indeed fit exactly - with 12 volts, however, nothing will be damaged, it simply doesn't work at all or the battery is not charged properly (and may then take some damage over time). But the 1 ampere is really only to be understood as a minimum: 14 volts with 2 amperes or 10 amperes or 5 amperes, it doesn't matter, everything fits. The power supply could then simply deliver more, but it only does so if the consumer wants it too.

      The mentioned monitor power supply with 14 V and 4 A or 2,7 A would be completely fine.

  7. Hello Mirco,
    First of all, thank you for the great informative site!
    Now to my question: I bought a small drone for my nephew. A USB plug was included for charging. According to the nameplate, the batteries require 7,4 volts. My problem:
    1. I am surprised that they are charged at all by the PC, since the USB connections run on 5 volts and
    2. Power packs for USB plugs with 7,4 volts cannot be found online.
    Since the manufacturer apparently "intended" charging with USB connections over 5 volts and this also works: Should I then just look out for a power pack with 5 volts?
    Thank you for your advice and continued success with the site!

    1. I would assume that the batteries should be charged in the drone - then the charging electronics regulate it internally and the voltage is transformed up.

      If you now want to load externally, it depends on the connection. I would bet on a rectangular, four-pin connector and normal LiPo batteries. There are inexpensive chargers for this, for example this no-name thing for around 17 euros on Amazon. These chargers are designed for 7,4 volt batteries (i.e. two standard 3,6 volt cells).

      And just to be on the safe side: The batteries should never be connected directly to a power pack! But only to chargers that don't just pump electricity in. Think of filling a water bomb: The human being is the charging electronics, so to speak - without human intervention the water bomb would simply burst at some point ;) And that can also happen with rechargeable batteries, only that it isn't funny then ... For the sake of completeness: If you did that, 5 volts would not be enough to fully charge 7,4 volt batteries.

  8. Hello dear Mirco,

    I'm having trouble finding a power supply, as there don't seem to be any 10V power supplies.

    It is a power pack with an output of 10V / 0,48A.

    Can I also use a power pack with 12V / 0,48A or is the lamp gone then?

    1. I'm afraid it wouldn't last long, with the 2 volts too much it could get very bright and very hot and then break. Of course, it depends on the lamp (i.e. the illuminant), but a good light bulb might still give you all sorts of hours of life, at least if it is not constantly on. How the associated lamp (i.e. the whole device) sees it is another matter - this could also be defective.

      But there are definitely universal power supplies with 10 volts. Here's one Sample device at Amazon for around 18 euros, which also has a cable clamp as an attachment, which makes it a little more universal.

      1. Thank you very much for the answer.

        I'm just wondering if the lamp won't shoot up anyway because 10V comes to 2A here instead of 0,48A as with the original power supply or does that not matter?

        And would the power pack with 9V / 0,48A be better suited and just a little darker?

      2. No, the 2A is not a problem, the lamp only draws 0,48A - the 2A is simply the maximum that the power supply unit could provide. And yes, 9V would definitely be the better option - damage would be less likely, but it could just be that it doesn't work in the first place. The lamp will almost certainly also work with 9V. However, if there is any electronics installed in the light (perhaps a clock, a loudspeaker, a timer or something), it could simply say “Nope, I want 9V” at 10V.

        I would try it with 9V if such a power supply is lying around, in the worst case it just doesn't work.

  9. I have a question about a power supply that I want to buy. My tablet needs 12V and 3A, the power pack delivers a variable voltage adjustable from 3V - 12V and has an output of 3A. But are these 3A also supplied from 3V – 12V or does this only apply to 3V and is reduced at a higher voltage setting, i.e. at the maximum voltage of 12V. LG Hans Martin

    1. Performance actually means watts - and this varies across the different voltages, in this case from 9 watts (3V x 3A) to 36 watts (12V x 3A). the amperage of 3A is available at any voltage. SatChef has a nice table with a fixed A value and the various V and W values ​​for a smaller power supply, which shows this again quite well in practice:

  10. Hi Mirko,
    Great article, that has helped me a lot.
    I have a laptop with an input of 19.5V and 11.8A, which is exactly what the power supply says as an output. (It's also the original power supply, so it should fit anyway)
    But now I need a new battery for the laptop and all batteries that fit the laptop according to the internet run with a voltage of 15.4V.
    I'm wondering if this is normal as the laptop may still regulate the voltage itself down, but I don't want to put in a battery pack that I'm not entirely sure I won't scrap both it and the laptop if I unplug it hang on.

    I've also looked at the type designation of the battery, but unfortunately I can't find any batteries.
    If it helps: I have an Asus Rog STRIX SCAR II GL704GV-EV013T
    The battery says C41PoJ5

    do you have any advice for me

    1. That's okay, the voltage for charging a battery is always slightly above its output voltage. For example, my Lenovo laptop has a 15,2 volt battery and is plugged into a 20 volt power supply. This then supplies the required charging voltage plus a little more for laptop electronics.

  11. Hello Mirco,

    just to be sure... my old charging cable broke, now I have another one to transition. The output of the charging cable is 19,5V and 10,3 amps. My laptop's input is 19,5V and 3,3 amps, so it should normally be fine right? Does that mean there should be no damage to the laptop and charging cable?
    Thank you in advance for your reply and your helpful report.

  12. Hello, Mirco,

    As an electrician, my previous search on the net was unsuccessful.

    I use an Amazon Echo 2nd generation exclusively as a loudspeaker in the mobile home.
    The original mains plug has an output of 21 watts and 15 volts. To do this, I first have to go through a voltage converter in the Womo, which I have connected to the cigarette lighter.

    I would like to supply the Echo with power via the USB output from the notebook or otherwise find a solution without the voltage converter.

    is there one

    Ask Martin
    and greets

    1. Unfortunately not really. There are converters for the USB port, but they don't achieve the required voltage or power. The USB specification just doesn't give anymore. Personally, I would get a power station for a mobile home without a 230V circuit. However, that would be an expensive solution just for this purpose: The smallest variant of anchor comes, for example, to 370 euros for 256 watt hours, i.e. depending on the echo performance maybe 12 to 2x operating hours.

      This would only be possible via the USB port of the laptop via a power bank: at least for the 1st generation Echo there was special external batteries, which in turn can be charged via USB. Of course, these things charge slower via USB than the Echo drains them, but depending on usage, that could be a workaround.

      times as Idea thrown into the room: Echo has two functions, speaker and voice assistant (Alexa). Alexa can also be used via smartphone, and speakers for the USB connection are a dime a dozen. So maybe just separate the two functions?

  13. Hello, great article... I'm a bit smarter now, but when it comes to electricity, I'm completely overwhelmed.
    I wanted to use a 12V cigarette lighter cable for a speaker (DC plug) as this is to be installed in the van.
    I was told that I shouldn't use the normal 230V plug independently, the on-board battery could run out too quickly.
    Now I'm looking for the right one.
    The original adapter says output 12 V - 2,5 A and 30 watts.
    I found a cigarette lighter with a double cable 2x 0,75 mm² and a barrel connector 2,5 x 5,5 mm with 12V 8A. Can I use that?

    1. Yes, that fits - the 12 volts match and more amps in the power supply is fine; the 30 watts required by the speaker easily cover the 96 watts of power from the power pack.

      Operation on the 230V mains is in fact not efficient, because the 12V of the battery is converted to 230V and then back to 12V by the loudspeaker power supply. Of course, it makes more sense to connect the 12-volt consumer directly to the 12-volt network. If the camper is somewhere connected to shore power, the regular 230V connection will of course also work.

      Happy camping!

      1. Hello Mirco,
        Thank you for your quick reply. Now I understand that the watts and amperes can be greater than the consumer, but the volts should be exactly right, right?
        Great, I'll remember that... I'd like to connect a few more things in the van, so this knowledge will definitely help me 😉... if not, I'll be back 😁
        Thanks and VG

      2. Hello, I have a lot of power supplies and don't know how to find out which device they belong to. How do I assign a power supply to a device. Many power supplies that I have come from somewhere and I have no idea where to assign all the parts

      3. Assigning power supplies to their actual, original devices is often difficult or impossible. You could try to search for any serial numbers on the power supplies on Google - at best this will bring up some product pages on Amazon, for example. And maybe you can then remember buying one of these products. Many manufacturers buy standard power supplies for their devices, so there can be several hits. More often, but probably none at all.

        But it's not that important! The only important thing is:

        • The plug must fit.
        • The voltage (Volt/V) must exactly match - and this is almost always written on both the devices and the power supplies.
        • The current (ampere/A) or power (watt/W) information on the power supply must be stated at least be as high as the corresponding information on the device (i.e. it can also be higher).

        If that fits, you can use the power supplies accordingly. Unfortunately, more allocation is not possible.

  14. Hi Mirco,

    I was looking for something specific, but couldn't find it.
    I have the following problem to solve.
    I have a battery charger without a power adapter.
    The power supply should be operated with 60W.
    However, the input voltage may be between 11V and 18V.
    What is the better solution now?
    An 11 volt power supply with 5,5A or an 18V power supply with 3.3A, or something in between.
    Specifically, the question for this case. Do you prefer more voltage or more current?

    1. Seems rather unusual to me, could not find such a device now. Actually, that shouldn't be relevant, only the 60 watts of power to be able to fully utilize the charger. In order to be able to say more, I would have to know the exact device with all the information.

      The only important thing is what the charger says about the output power, i.e. which batteries can be charged - it doesn't matter how exactly the different input voltages are regulated internally.

      The caveat is that there are the most obscure devices that do the most obscure things...

      1. Hi Mirco,
        First of all, thank you very much for your quick reply.
        I got myself a SKYRC iMAX B6 Mini.
        A colleague has been using this device for some time to charge 100AH ​​LiFePo4 batteries etc. That's why I bought it now, because it also has NiMH, NiCd and lead batteries on it. :-)
        Only if I get a new power supply anyway, or use one from my inventory, then I want to get the most out of it. Hence the question of what is better. More current or more voltage. But if the bottom line is that it doesn't matter and the only thing that matters is the maximum performance anyway, it's much easier anyway.

        Greetings Alex

      2. Ahhh, okay... the device falls a bit outside of my experience. But it's exciting. As far as I can see from the manual, the part is primarily intended for use with a car battery, hence the bandwidth. I would say it doesn't matter, I couldn't find anything else - the performance just has to be right.

        Small I-am-not-an-electronics-nerd disclaimer: I can't say whether measurements might reveal differences in the efficiency of the charger or other "internals". It is quite possible that a theoretical physicist has a different opinion than a pragmatic electrician ;)

  15. Hello Mirco :)
    Great article and helped me a lot even though it's 8 years old. When reading through it, I was surprised that after such a long time people were still writing to you and asking questions, even though everything was actually explained clearly ... I thought :) Because if you look at the questions, most of them are really justified and that's how it is gone to me now too.

    Here's the thing: I just bought a used Akai MPC Live. Super device in top condition :) So far I've only used it once with the power supply and charged it once. Thank God for your article :) Because the power pack has 24V output (at 2,71 A), but the device only requires 19V input (at 3,42 am). Judging from your comments the difference is huge and should have blown the unit long ago and since it's used I don't know if that was the original power supply that came with the machine.

    But now my question: If I calculate the watts then I get about 65 watts for both. Does this mean that despite your rule that the volts must match exactly, the power supply and device are perfectly matched and I can use the two together?

    Thanks for your help and all the best from Zell am See :)


    1. Nice thought, but unfortunately no, the right number of watts is not enough. You even have two possible sources of error: Too many volts could fry the beautiful MPC and too few amps could damage the power supply (in the long run).

      That's always all subjunctive ;) The Akai MPC Live II isn't a cheap "Chinese junk" but high-quality hardware. So I would guess that there is just a little more leeway to dissipate the excess tension to some extent in the form of heat. With a fully charged battery and in continuous operation... - I wouldn't risk it with an estimated 700+ euro expensive device. Especially since it's available on Amazon for 20 euros suitable power supplies gives.

      My problem is much worse there, now I want to have an MPC next to my cheap Akai MPD 232 ;)

  16. Hello Mirco, I'm a real idiot when it comes to everything that has to do with electricity :-(
    With my power pack from Fanatec (steering wheel for PS), the cables are stripped, I have no idea how - it says on the power pack
    Endors 6200
    Input 240V, 50/60Hz, 3,0A max
    Output 24V, 7,5A, 180 watts
    I found a replacement power supply that only delivers 5A, does that work?
    Thanks in advance!! :-)

    1. Rather not, 5A instead of 7,5A delivers far too little power. It's possible that the steering wheel works and only the feedback motors in the steering wheel don't run or hardly run at all - but that wouldn't be fun either ;) In addition, the power supply would constantly run at the limit and suffer damage itself, or it would simply stop working. Means: The power pack must deliver exactly 24V and at least 7,5A. That's 180 watts, unfortunately there aren't that many universal power supplies of this size, especially since the plug still has to fit...

      1. Thank you for the quick reply, now I'm a little smarter ;-)
        Yes, the exact same power supply is hard to find...

  17. Hi, nice article, but I also have another question. I bought a new socket with USB-A and USB-C connection.
    USB-C says: 5V / 3A
    The device that is supposed to ran there has so far run via a Schuko adapter (standard Samsung) and the device itself says 9V 2,77A.

    I thought of asking because one of the reviews reads:
    Good product but the USB-C doesn't have enough power for an Apple HomePod. This is a pity.

    Does that mean it loads everything, but just slower?

    Thanks in advance :)

    1. That depends on the device. First of all, you have 15 watts of charging power on the USB-C. The HomePod Mini uses 20 watts. In principle, a power bank or a smartphone/tablet would charge more slowly on the port than with a power supply unit that has 20 watts, for example, but significantly faster than with the classic 5V/1A power supply units that used to be included with iPhone & Co.

      1. As a small addition: rechargeable batteries are sometimes finicky, too little voltage can lead to more problems, such as a drop in performance. A fan with too little voltage would simply run slower. So, if it's something really expensive where battery life is important, I'd look for a proper charger.

  18. Hello Mirco and thank you very much for the article. At least that helped me not to order the wrong thing. Since I'm technically very inexperienced, I prefer to ask here again (for dummies ;-) ).
    I bought a Thunderbolt Dock without a power supply, or he simply didn't deliver it ;-(. The device says 20V 9A on it. You could use it to charge a laptop via USB C / Thunderbolt, for example. But I don't want that at all. Me Thunderbolt / USB C is sufficient without power. But if I understood you correctly, any power supply with less than 9A would break if I attached it, regardless of whether power is tapped off again or not. Correct?
    My problem at the moment is... I can't find a universal power supply with this information and the right plug (or a selection of plugs) with the best will in the world. So I'm also happy for any tip where I could find something like this. PS The model is a Kensington SD5700T and no, unfortunately the manufacturer cannot supply replacement power supplies.

    1. Rather not. If a power supply does not deliver enough power AND is cheap junk AND actually draws a lot of current, it could burn out. Usually there are protective mechanisms in there. I would still keep an eye on the heat development. But the dock hardly draws any power itself, but more or less passes it through - if nothing is connected to it, it should work. However, it could of course be that the electronics are on strike due to incorrect specifications. So far, however, nothing would break.

      Whether the part can then "USB without power", how the ports on the dock are set and what exactly the notebook and its Thunderbolt connection would say about it, especially since I really have no idea about Apple (?), I can't either to say. I would just try, something worse than nothing happening at all I think is unlikely.

      The 20 volts should of course be given and the closer the part is to the 9 amps, the better. But since the part can supply quite a few things with electricity at the same time, it could also run with significantly fewer amps.

  19. Hi, I'll join all the questions.
    I lost an old portable DVD player and power adapter.
    The data I can read from the back:
    Power Source: DC 9,5Vm
    Power Consumption < 25w

    In my ignorance, I would just buy a universal device and operate it with 9V, because apparently there aren't things with 9,5.
    Something here: https://www.amazon.de/AmazonBasics-Universal-Steckernetzteil-abnehmbaren-3-12-Gleichspannung/dp/B07DNKMRP3

    Maybe you can give me a tip :)
    Thank you!

    1. So the half volt less voltage in the power supply is not necessarily a problem, it does not damage the device - it just might not work. So you can just try it. But don't be surprised if the player crashes or produces errors at the performance limit (high volume, bright display). The type of device doesn't really sound like the warranty is still running ;) - but just in case: If you use it outside of the specifications, you could probably bend it. What will not work: Charging batteries.

      However, the linked power supply only has an output of 6 watts, so the 25-watt DVD player will probably say no.

      This one is built similarly and has 27 watts for 5 euros more. I don't know it, it was simply the first model of this type.

      1. Hey,

        I have a 32″ tv with 19v and 3,0A… can I connect a power supply (specified for notebooks) with 19,5V and 4,25A?

        Thanks in advance :)

      2. The 4,25 amps are perfectly fine. 19,5 volts are half a volt too much – it can work well, it probably will, but it could also wreck the TV ... As I said, it's rather unlikely at half a volt, but of course any guarantee is gone. If you try it: At least keep an eye on the TV to see if it is getting really hot when connected to the mains. Personally, I wouldn't leave the thing unattended for long periods outside of the intended specs either. The better the TV (branded device?), the lower the risk of serious damage. Otherwise: Universal power supplies with 19V and at least 3A are available from around 20 euros and up.

  20. I have a device with a DC input with 4 R6 on the device says 6V input and 1,5A. Can I take a battery with me there
    Connect 6V 4,5A. An operation for external supply is provided by means of a barrel connector.
    I'm not sure at the input for the barrel connector it says 6V 1A are the 4,5A of my battery too much?
    Thank you for any answers

  21. Hallo,
    I have a thermometer with 2 x AAA batteries.
    I would like to replace this with a DC transformer 3V and 1A.
    Would it work, or do I need a series resistor before the connection?
    If so, what should the resistance be?
    Thanks in advance,

  22. Hi!
    Great site and great article, thanks for that – now even I understand it so far.
    However, I'm at a loss with the power supply that I have to replace and can't find a replacement (or only from the UK and super expensive):
    INPUT: AC230-240V~50Hz 20mA
    OUTPUT: AC11.5V~1600mA 18.4VA
    I was told I could also use a 12V 1500mA - is that true so far?
    Is there a recommended forum for such questions?
    Greetings from Cologne, Daniel

    1. So since the deviation is relatively small, it could work - but it depends on the exact consumer and the exact power supply. 0,5 volts too much does not have to harm the consumer and the insufficient power from the power supply does not have to harm the power supply - but both can stop. For most devices, I would personally bet on a manageable risk, but stick with the tapping...

      You will only find precise information in forums that are either explicitly about power supplies or about the type of consumer - it makes a difference whether a robust fan gets 0,5 volts too much or a sensitive electronic device that, in case of doubt maybe shuts off immediately if it's not exactly 11,5 volts. And a cheap PSU could very well get a loooooooooooooooooooooooooooo warm when running at full load continuously. Actually you only have two options: risk or find someone who has experience with exactly these devices.

  23. Can I use a 20V/3.25A power supply for a Pioneer 18V/3.6A system. The power supply fits, the system also turns on. LG and thanks for the answer in advance…….

    1. I would advise against it. The power supply has 20V, but it should have exactly 18V - so something could burn out. In addition, it also delivers too few amperes, here the value should be above the 3,6A from the consumer. Less tragic for the system, but the power supply could get too warm. The values ​​are close, if the system and power supply are good, it could work with luck, but it doesn't have to. In any case, I wouldn't let it run unnoticed ;)

    1. Um, so if you put the Input by the consumer mean: no. The power supply outputs 9V, the consumer would like exactly 6V and would then probably burn out with 9V.

  24. Thank you for the contribution! I've come a long way now.
    However, I still don't know how I know what voltage I have to set on a universal power supply.
    I have the following data at my disposal
    Input 100-240V 50/60Hz 1000mA
    Output 24.0V 1500mA
    It would be great if you could help me with that!

    1. With a universal power supply you have to set the number of volts that the consumer needs. The specified values ​​now only say output 24 volts - but there will certainly be more options as a universal power supply. In addition, one would have to know what is written on the consumer. The input part just says what the power supply itself consumes at maximum and is not really relevant here.

      Basically it's very simple:
      V/Volt must be specified for the power pack and consumers exactly to match.
      A/Ampere must be at the power supply at least be as large as the consumer.

  25. I have a question, can I charge an Airiton&BAOFENG UV-S9 Plus 7,4 volt with a solar panel like the "BigBlue 28W portable solar charger" (5V/4A) or the "OUTXE Waterproof Solar Power Bank 20000mAh"? Sorry I don't know much, thanks in advance!

    1. No, the radio requires 7,4 volts and that has to match exactly. The solar panel can only 5V and the power bank 5V, 9V and 12V. When it comes to ampere values, power banks & co. can easily be higher than the value of the consumer, the volts have to be exactly right. And I suspect that 7,4 volt power banks or solar panels are not that easy to come by.

      1. Ah, sorry, I was operating it, charging is another thing, I overlooked it... The battery delivers 7,4V, but can be charged with 5 volts, so yes, the devices fit together (thanks to standardized USB).

  26. Hi.
    I am looking for a power supply that is no longer available on the market and has the following specifications:
    Input ~ 230V 50/60Hz 10VA
    Output 2V ⎓ 350mA
    The universal power supplies I've found only start at 3V output though. Would that not possibly scrap my Walkman?
    Or what other power supply could I use otherwise?
    Thanks in advance !

    1. First of all yes, that would possibly break the Walkman, personally I wouldn't risk it - although good hardware might endure it...

      Spontaneously I did not find a normal 2 volt power supply, actually seems at least rare. I'll look again later, only laboratory power supplies come to mind quickly, but 70 euros aren't exactly cheap and they certainly won't get much cheaper.


  27. Looking for an old mind activator power supply with 9v/220v. There are often so many numbers on offers that I don't know what I need

  28. Hello Mirko, I am looking for a replacement power supply for a laptop. The original power supply says:
    Input: 100-240V-50/60Hz, 1.8A
    Output: 5V=2A or 9V=2A or 12V=2A or 15V=3A or 20V=3.25A
    My question: how many volts does the replacement power supply unit need? And: Is there anything to consider for the input with 1.8A?
    Thanks and regards Ashley

    1. What voltage does the laptop require? 5, 9, 12, 15 or 20V ??
      I'm guessing 19v...
      Input doesn't need to be considered, but it should be able to supply the power that the laptop requires. This is usually on the nameplate / sticker.

    2. Sorry, just saw this - Sam is right, input is not important and volts depend on the laptop. If the power supply does not have a switch for the different outputs, this is probably automatically negotiated with the consumer - that is to say, the manufacturer probably uses the power supply for different laptops. For your specific laptop you need one with the appropriate voltage - as Sam already wrote, to be found on the type plate. Otherwise: google the model, or leave a comment here if you are not sure.

  29. Hello everyone, I have 2 x 12v 5a power supplies, what kind of power supply do I need to run both over one? They are aquarium lights, thank you in advance for your help

  30. The power pack for the charging cradle of my cordless secateurs has burned out. The battery says 18V, the charging cradle and power supply say 20V each. I have already tried different power supplies with 18-20V, but the battery is not charged properly. The measurable voltage of the battery increases to 20V, but when I use it, it is empty after 3 seconds.
    I suspect that the power supply and charging cradle provide more than 20V. Which power pack with how much real output voltage should I use (without the charging cradle burning out) so that the battery can be properly charged again?
    The problem is that the original power supply is no longer available.

  31. Hello Mirco,

    I also have a question:
    I have a small 12V pump that says it is operated with 3,5A but max. 7A. Now I need a transformer for this and have ordered one with 5A. Is that enough, or is the pump simply not working?


    1. Hmm, I've never seen it like this, but it will work - just not at full power. If the thing runs around the clock, I would initially check every few hours to see if the power pack isn't getting hot - just in case the internal control of the pump is defective or the power pack can't stand permanent full load (which actually only with the cheapest garbage and even then very rarely should occur ;) ). If the pump has a regulator for the power, it should of course be regulated down accordingly.

  32. Hi,
    I have an intercom in the house of Femax. It consists of 3 phones with a monitor. The power supply for this is provided by two power packs. each: input 230V AC voltage and output 18V DC voltage 1A.
    One of them is defective. I need to order one urgently.
    The power pack with an output of 18V direct current and 1A is no longer available.

    The new power supply that is currently available has an output of 18V DC and 3,5A.

    Is that in order??? can i order this

      1. It happened to me once, I had a universal power supply and accidentally set the wrong voltage, then the device melted away. Luckily I noticed it quickly, otherwise worse would have happened quickly.

  33. What about model railway accessories?
    I have 25 decoders with 12V and 2A each, do I have to calculate 25 times 2A or is a power pack with only 12V 2A enough?

    1. I have no idea about model railways and decoders and what they do or how they are connected... But if they are all blowing 2 amperes somewhere all the time, you would indeed need a 12V and at least 50A power supply.

      For example like this here with 600 watts.

  34. what does it actually look like with a controller that runs with usb power but only half-heartedly, on energy-saving lamps led lighting so to speak, which is also supplied as standard without a power supply, but has a 15v and 1,2A connection. Because there is no more information , you should think, you can easily assume that all 15V power supply adapters that are offered on the net should all fit in principle...from a certain volt number onwards, power adapters all have the same connector shape, or you buy them there still on the off chance? because I don't have to pay another 25 for an adapter, even if I can get one for €9,95?! I assume that the answer will be something like this, if you want to be on the safe side, buy the one the manufacturer of the controller offers...lol you finally save a few euros by changing your electricity provider, buy a power adapter and bubb, nothing remains of the profit, except for a power supply ????????????

  35. It should be added that many power supplies for modern devices have a tolerance for the number of volts and work in the range of approx. 100 to 240 volts, which is why they can also be used with a simple plug adapter in the USA, for example, where approx. 110 volts ( instead of the usual 230 volts here) from the socket. Charging cell phones and laptops is therefore not a problem there. Conversely, you have to be careful, since American devices are often only designed for their area and a cheap plug adapter is not enough. Fortunately, suitable transformer adapters can be bought in this country.

  36. A tricky question: I have an old, intact network switch where the power supply is missing due to moving, a no-name product without any documentation, and it doesn't even say what voltage the power socket has on the housing or on the sticker wants. Google doesn't help me because the product no. is unknown. Comparable devices have 12V - 1 A. The only idea I have is to "work my way up" with different power supplies, i.e. 5V first, then 7,5V / 9V / 12V. This is cumbersome, however, because it is only during operation that you can see how stable the switch is.

    Does anyone have any other idea how I can find out?

    1. That is absolutely correct. The first version of the article contained a transposed digit, which was then corrected by a colleague into a correct calculation, but with the "wrong" values ​​(see above in the comments). I'm just not a fan of changing so much afterwards that it's no longer possible to understand the comments. But okay, I'll rewrite it. Thanks for the hint!

  37. 10.03.2018

    I have a 12 volt car wiper motor and would like to use the geared motor for another purpose, I estimate the wattage to be between 35 - 55 watts, the motor is from a Ford.
    I'm looking for a small switching power supply (230 V input, 12 volt output. Who can help me with this?

  38. What does the difference between input and output voltage on the power supply say if we are only interested in the output voltage values ​​in relation to compatibility?

    Current topic for me: Input voltage: AC100-240V 50 / 60Hz Output voltage: DC 6V / 2000mA is written on the back of a headphone amplifier that I want to use on the PC, so I have to have a 6V/2A power supply, ok. But what information do I get from “Input Voltage”? In addition, a customer of the headphone amp wrote that he operated it with a power bank that only outputs 5V and 2 or 2,4 A, how is that actually possible? Does the ampere value actually increase proportionally to the V value, i.e. at 6V, more than 2-2,5 A can never flow? Or is it? If yes, why? greeting!

    1. No, how much current flows, i.e. how many amperes flow, depends on the resistance R. You calculate this with resistance=voltage/current. The amperage is calculated with amperage=voltage/resistance.

  39. Hello Mirco,
    My laptop's power supply is rated at 19V. I still have a power supply from an old laptop that says 20V. I would now like to use this to be able to operate the device in two different places in the house, the battery is no longer the best. Because it actually only charges the battery and does not supply the hardware directly, the difference of 1V should, in my opinion, be easily within the tolerance. Amperage is almost identical, connections the same. Still, I'd like a second opinion before I get infected, what do you think?

    1. I'm definitely not enough of an e-technician to give a really experienced answer, but I wouldn't risk it - cheap components in particular can quickly be finicky. And since I myself once shot a camera because of 3 volts too much, I'm also moderately keen to experiment. 19 V power supplies are available for around 10 euros on Amazon - it's not worth risking the computer.

  40. I have an original 220 volt power supply that lets out 19 volts/3A at the output.
    Since I now want to operate the device to be charged in the car, I ordered a converter from ebay that converts DC12Volt to 19Volt/4A and lets it out at the output.
    Does the amperage play a role and can I damage my device to be charged with this converter?

      1. If you're already pooping currants, please do it correctly: A normal power supply has 5V not 0,5V - i.e. 3,5 watts were right, somehow.

      2. The article still contains the said 0.5V - which is probably why the note. wasn't entirely inappropriate...

        Anyway thanks and have a nice weekend

      3. That's right - the article now contains a correct calculation, thanks to Christian's correction, who made the correct 3,5 watts out of 0,35 watts. It would have been even better to leave the 3,5 watts and correct the other values ​​- then it would not only be a correct calculation, but a correct calculation with plausible values.
        If I were to completely rewrite the calculation now, all the comments would be obsolete ;)

  41. It should probably be added that amperes are current (A), volts are voltage (V) and watts are power (W). The values ​​can be converted into one another: 1 A = 1 W per V, i.e.: A = W/V. In this way, missing information on power supplies can be added.

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