Long time programmer starting to learn about electrical engineering a little bit. I have a Raspberry Pi, an Arduino, and various simple projects I've soldered together out of kits and schematics friends have given me.

Recently I moved and lost many of my AC adapters. I found I was able to use different ones from other devices. AC adapters from devices such as the original kindle, old accessory USB AC adapters, old and new Apple AC adapters, and many others that do not have a USB input but rather the older style (I forget the name of the connector on the end, some sort of DC power connector Arduino UNO's have one).

So an example of what I'm asking is this: What effect does it have using say an Amazon kindle AC adapter (or any other mismatched brand adapter) with an iPhone lightning to USB cord?

Specifically, my Arduino/Raspberry Pi are using random usb min/micro cables plugged into completely random AC adapters. Most of which have no indication of their specifications. What effect could this have? I have another dubbed a "Fast Charger" that puts out (from what I can tell) 2-3 amps based on the voltage.

Another example would be the Arduino DC power connector, I also have the same connector on a small breadboard power supply. I find anything that fits seems to work in there. What effects might this have?


  • 3
    \$\begingroup\$ This probably answers most, if not all of your questions. \$\endgroup\$ – brhans Nov 12 '18 at 17:54
  • 1
    \$\begingroup\$ Possible duplicate of Choosing power supply, how to get the voltage and current ratings? \$\endgroup\$ – JRE Nov 12 '18 at 18:25
  • \$\begingroup\$ I read that answer and while they’re close I wouldn’t call them duplicates. I was asking about the possible effects not how to choose. Since the other post alone did not fully answer my question I believe it is worthy for both sources of information to exist within SE. \$\endgroup\$ – shenk Nov 12 '18 at 18:27


Different adaptors have different voltages. You must use the correct voltage (within the margin of error which is hopefully written on both parts). If you don't the consequences could vary from it working, but unreliably, to not working, to immediately and permanently failing, to catching fire.


Some connectors, such as the barrel jack connector on the arduino, come in different polarities. e.g. "Center pin positive" and "Center pin negative". Getting that wrong can have similar consequences to the above. Other connectors, such as the various versions of USB, only have one polarity, so it doesn't matter.


The power supply will have a maximum current it can supply, and in some cases also a minimum. The load defines the actual power drawn, and as long as it is in-between the maximum and minimum for the supply, all is well. Otherwise, it will probably just not work. It is in theory possible to damage the supply this way, but that only usually happens with rough and ready supplies, or those designed for building into products, not the ones which come separately.

Isolation and Grounding

For safety reasons, you must not swap isolated and non-isolated power supplies, though from your description all yours will be isolated. You should not swap grounded and non-grounded supplies either, though the consequences there are less severe.

Power supply connectors

It sounds like many of your supplies have USB connectors. That's good, as they will all be 5V, same polarity, isolated, and almost always floating. This is because USB chargers are standardised. The only variation will be in the current they can supply, which hopefully will be written on (watch out for cheap ones with lies written on). And if you try to draw more current than they can supply, they will shut down safely. The ones with the barrel jacks will be more variable, as there isn't a standard.

| improve this answer | |
  • \$\begingroup\$ Amazing answer. Could you possibly give me an example of where one would run into non-isolated and grounded/non-grounded supplies? \$\endgroup\$ – shenk Nov 12 '18 at 17:56
  • 1
    \$\begingroup\$ Non-isolated supplies are cheaper to make, but it is possible to get a mains shock from the outputs. They are normally only seen sealed inside insulating plastic products, but might also appear on rather old products in countries with polarised plugs. Grounded vs floating is more complicated and would be a design decision made to reduce electromagnetic noise. Floating is more common, as it is simpler and cheaper. Grounded can help reduce electromagnetic noise issues, but only works in countries with grounded outlets, so designers often choose a different solution. \$\endgroup\$ – Jack B Nov 12 '18 at 18:02

Not the answer you're looking for? Browse other questions tagged or ask your own question.