As long as the plug fits, are all AC power adapters interchangeable? I have several adapters, and have lost track of which devices each is for. Can I use any one with any device? If not, what determines compatibility?
What matters is the voltage. Every wall-wart will say on it how many volts it outputs, and every device will list somewhere near where the plug goes in how many volts it needs. Those need to match.
The current output is also important, but less likely to be relevant. Every wall-wart will also say how many amps it can output. Every device should likewise say how many amps it will draw. As long as the device’s current draw is less than the adapter’s current capability, you will have no problems. If the device’s draw is greater than the adapter, then if it’s a battery charger, it’ll probably just charge slower, though in other cases you might potentially damage the adapter.
Sadly no, there is essentially no standardization of barrel-plug compatibility between different AC adapter manufacturers. Keep in mind also that some wall-warts are AC transformers and others are DC power supplies.
The only way to be sure is to read the power input labeling on your device and match it with the wall-wart in question.
Another thing to check is the polarity, whether the center is positive or negative.
No, they are not interchangeable.
The first thing to look at it does the plug fit.
Most AC adapters have a co-axial plug with two conductors. So the next thing to look at is whether the inner conductor is the positive or the negative conductor, often referred to as tip positive or tip negative. They may use words to describe which it is, or they may use a symbol that looks like this:
The one on the left shows tip positive and the one on the right is tip negative.
The next thing you want to look at is whether the output is AC or DC. Most AC adapters convert the voltage to DC, but there are some that are just AC transformers.
Then you want to look at the voltage. This has to match pretty closely. How closely depends on the device. I have an electronic keyboard that can take anywhere from 6 to 12 volts. Many other devices will fry if you give them double the voltage like that. If the device takes 12 volts and the adapter is 12.6, then that’s probably close enough. If the device takes 12 volts and the adapter is 18 volts, you’ll probably damage it.
All of the above has to match pretty closely.
The last thing to look at is the current, which will often be in either milliamps (mA) or amps for something that draws a lot of current. This one you don’t have to match exactly, but the adapter has to put out at least as many amps as the device needs. If your device is 12 volts and 500 mA, you can use an adapter that has higher mA, like one with 750. The device will only draw 500 out of that 750. You can’t use an adapter with lower current though. If you try to use an adapter that is 12 volts and 250 mA in this example, the device will try to draw 500 mA from an adapter that can only supply 250 mA, and the adapter will fry, maybe taking the device with it.
You don’t want to go too much higher on the current though. A lot of adapters don’t work properly if they have too small of a load, so an adapter that is rated for 2 amps (2000 mA) may not regulate itself properly with a load of only 100 mA on it. The output voltage may swing wildly or do weird things and the device could be damaged.
So in summary, the plug, polarity, and voltage all have to match, and the current in the adapter has to be greater than or equal to the current needed.
In the future, you might want to do what I do, and write the device name on the adapter with a silver sharpie, as soon as I unpack it.
The next thing is that the cheap wall-warts output dirty, barely regulated power. This is suitable for tasks like charging a lead-acid battery but not for running your tablet. So even if the voltage and currents match, it may not work correctly - the expensive walwarts have linear regulators and sometime devices require them to operate correctly.
Most of the biggies (voltage, amperage. polarity) have been civered,
For the really bizarre: the “DC” put out by those ‘wall warts’ is DC in name only.
If you have a circuit that uses batteries, do NOT assume a wall wart of the same voltage can be substituted. Maybe it’ll work, maybe, like me, you’ll fry the device (an electronic circuit) with the ‘dirty’ wave form.
And then there are regulated vs. unregulated supplies…
I’ve heard that this is a big issue with generic USB chargers, especially the ones that are designed to look like name-brand ones but aren’t. The actual name-brand ones, though, are usually pretty good.