When you're working on your robot you'll likely want to plug it into a wall socket rather than run it from batteries. For that you'll need a reliable __USB Power Supply__ with enough current capacity to run your
processor (e.g., [Raspberry Pi]), your [sensors], [motors] and any other accessories (such as displays).

We'll focus on the [Raspberry Pi] since it generally requires more power than other [microcomputers/microcontrollers|microcontrollers].

!! Dishonest Advertising

There are a number of companies providing USB Power Supplies specifically for the Raspberry Pi. Each of the
different Pi models has differing power requirements, but at least a __3 amp supply__ is probably recommended.
The problem is, the companies selling these units are not very honest about the power ratings of their
products. Apple is by far the worst: they sell two adapters (listed as the ''Apple 87W USB-C Power Adapter'' and the ''96W USB-C Power Adapter'') that are likely the most expensive on the market and are not showing their output ratings in watts but seemingly their power requirements, i.e, not what they __deliver__ but what they __use__. Of course it says nothing about this on the box. 

I made the mistake of buying the 87 watt unit for NZ$120 (wow!), opening the box and finding in fine grey print on the adapter a confusing bunch of different amperage ratings at voltages, but at 5 volts the unit delivers 5 volts at 3 amps. To give you an idea of how far this is off from that advertised 87 watt promise, delivering 87 watts at 5 volts should be showing __17.4 amps__. Apple are clearly using 87 watts to deliver 15 watts (3 amps at 5 volts) of power. You can check this yourself by using an online 
[Watts to Amps Calculator|https://www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.html]
or [Amps to Watts Calculator|https://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.html].

This is where having a bit of your own knowledge is good. These are the two pertinent formulas:
{{{
  amps = watts ÷ volts
  watts = amps × volts
}}}
If the Raspberry Pi people way your Pi needs 3 amps, that's not how much power the adapter is using, it's
how much it's delivering.

----

[{}]