Power supply

A power supply is hardware (typically analog, although more modern units often include digital sections) which converts incoming power (often line-voltage AC from the wall supply) to power (usually DC) at the voltage(s) and current(s) needed for other circuitry.

In addition to simple conversion, power supplies usually place some constraints on the quality of their output (ripple, etc); they also often include large enough capacitors to 'tide over' power spikes on the input supply.