Taiwan & China Reliable Power Supply Manufacturers & Suppliers
Short for Power Supply and sometimes abbreviated as PSU, which is short for Power Supply Unit. The PS is an internal hardware component used to supply the components in a computer with power by converting potentially lethal 110-115 or 220-230 volt alternating current (AC) into a steady low-voltage direct current (DC) usable by the computer. A power supply is rated by the number of watts it generates. For example, the image to the right, is of an Antec True 330, a 330 Watt power supply and an example of what a computer power supply looks like.
Do not open the power supply, it contains capacitors that are capable of holding hold electricity even if the computer is off and unplugged for a week, if not longer.
On the back end of the power supply as shown in the above picture is where you connect the power cord to the computer. In addition to the power cord connection the back also has an fan opening to draw air out of the power supply, a small red switch to change the power supply voltage, and the rocker switch to turn the power supply on and off.
source: Computer Hope: Free PC Helps & Info