Power Supply EditBy Galena Cox
The power supply, also called the power supply unit (PSU) takes the power from the outlet and converts it into the correct amount of power for the specific parts of a computer. The PSU must be compatible with the motherboard and the case to which it connects. The PSU is located inside the case of the computer. The PSU has a three pronged plug that extends from the case of the computer. The plug connects to a power cord from the power source. This brings the raw power (the power from the power source, generally a wall outlet) to the PSU. The raw power is AC power which stands for alternating current. The PSU converts the AC power into DC power. DC stands for direct current. The parts of the computer including the CPU and the HDD work using DC power. The PSU connects to the parts of the computer through many colored wires.
The PSU not only converts from AC to DC power, it also changes the voltage of the power to give the correct amount to each part of the computer. For this reason the PSU is also called the "switching power supplies". The PSU converts the AC power to a lower voltage. It typically switches it to 3.3, 5 or 12 volts. 3.3 and 5 volt DC power is used by the digital circuit. the 12 volt power is used to motors such as the motor in the fan.
The power that the PSU supplies is measured in watts. Older PSUs supply most of the power in 3.3 volt or 5 volt watts as opposed to modern PSUs which send out 12 volt watts. Years ago, computers had a switch on the outside of them that one switched on or off to turn on or off the computer. That switch controlled the flow of AC power to the computer. Thus flipping this switch cut off all power to the computer.
Before 1980 the PSU was very large. Transformers were used to convert the power AC power to DC power and to lower the wattage. Today, the PSU is lighter and can convert power much more quickly. Although sometimes taken for granted, the PSU is an essential part of the computer; the computer cannot work without it!