@MissConstrue Also the short intro is ohm's law: https://en.wikipedia.org/wiki/Ohm%27s_law And it's mostly unit conversion: I have volts and amps, I need power, look up on the chart for how to convert. And that bad things happen if limits are exceeded. This cable is only designed for 5 amps, but because the designer was an idiot and didn't limit current a device tried to pull 10 amps and ended up melting the cable. (It's more complicated in that the cable has resistance which means more power dissipation at higher currents and more power means hotter, and there are tables for these limits from past experience.)