A power switch controls the flow of power to an electric device. The switch has an on and off position, usually represented by a 1 (on) and a 0 (off).
Every computer today uses a power button for turning on and off a computer. However, many desktop computer power supplies also have a power switch, as shown in the picture. This power switch turns on and off the power supply, and if set to the off position, the power button for the computer does not work.