Computer power supply

A computer power supply typically is designed to convert 120 V or 240 V AC power from the electrical company to usable power for the internal components of the computer. The most common computer power supply is built to conform with the ATX form factor. This enables different power supplies to be interchangeable with different components inside the computer. ATX power supplies also are designed to turn on and off using a signal from the motherboard (PS-ON wire), and provide support for modern functions such as the Standby mode of many computers.
Computer power supplies are rated for certain wattages based on their maximum output power. Typical wattages range from 200 W to 500 W, although some new personal computers with high energy requirements may draw as much as 1000 W (1 kW).
Most computer power supplies have a large bundle of wires emerging from one end. One connector attached to the opposite end of some wires goes to the motherboard to provide power. The PS-ON wire is located in this connector. The connector for the motherboard is typically the largest of all the connectors. There are also other, smaller connectors, most of which have four wires: two black, one red, and one yellow. Unlike the standard electrical wire color-coding, each black wire is a Ground, the red wire is +5 V, and the yellow wire is +12 V.
Inside the computer power supply is a complex arrangement of electrical components, ranging from diodes to capacitors to transformers. Also, many power supplies have metal heatsinks and fans to dissipate large amounts of heat produced. It is dangerous to open a power supply while it is connected to an electrical outlet as high voltages may be present even while the unit is switched off.
In desktop computers, the power supply is a small (PSU) box inside the computer; it is an important part of the computer because it provides electrical power in a form that is suitable for every other component inside or attached to the computer in order for it to work. If only a small voltage is needed, the mains power needs to be transformed to a suitable level in order for the component to work.
In portable computers there is usually an external power supply that produces low voltage DC power from a mains electrical supply (typically a standard AC wall outlet). Circuitry inside the portable computer uses this transformed power to charge the battery as needed, in addition to providing the various voltages required by the other components of the portable computer.
Power supply main connectors come in two types. The older main connector can be a 20-pin, which works primarily with ATX boards based off of the 478 Socket for Intel boards. The current and newer boards are based off of the Intel 775 Socket use a 24-pin Connector or the 20+4-pin connector on PSUs. Most socket A AMD motherboards use the 20-pin conector, but a mixture of 20-pin, 24-pin and 20+4-pin conectors are used in the AMD range of socket 754 and 939 pin motherboards. However, almost all motherboards from AMD's new AM2 940-pin socket need a 24-pin or 20+4-pin connector.