A power supply unit (PSU) is the component that supplies power to the other components in a computer. A power supply unit is designed to convert general-purpose alternating current (AC) electric power from the mains to usable low-voltage DC power for the internal components of the computer. The most common computer power supplies are built to conform with the ATX form factor.

Picking one

This can be one of the hardest parts to choose.

There are numerous factors to choosing a PSU. This is were Antecs free Wattage calculator http://www.antec.outervision.com/ comes in handy to find out what is a recommended top wattage your PSU should sustain. There are also some main things you should look at before purchasing.

First off, buy a decent brand name. No-name PSU's are generally inferior and if you plan on making your PC work for its keep (pushing it hard, leaving it on 24/7) then it's false economy. Also, try to get a PSU that has a 12cm (4.8") fan which doesn't need to rotate as fast to keep the PSU cool, making it a lot quieter.Also keep in mind when purchasing a PSU unless you buy a high end power supply the PSU will only really likely to give you, at best, 75-80% of the power they claim, this is why it is good to go 100 watts or more above the bare minimum of what you are recommended. It is also proven that PSU are most likely to fail if they are constantly under 100% load so save yourself the expense in the future and invest with a PSU with more breathing room.

Modular Cabling

A modular power supply lets the users to omit unused cables. Whereas a conventional design has numerous cables permanently connected to the power supply, a modular power supply provides connectors at the power supply end, allowing unused cables to be detached from the power supply, producing less clutter, a neater appearance and less interference with airflow. It also makes it possible to supply a wider variety of cables, providing different lengths of Serial ATA power connectors instead of Molex connectors. These are useful in some applications, if you are not pressed for space however i advise going with non-modular cabling for the simple fact that they are usually sturdier connections and cause less electrical resistance.

PSU Checklist

1. Buy quality name brand, read reviews.

2. Leave some breathing room, get more wattage then required for expansion and so you are not at 100% load.

3. Make sure you have all the Pin connectors that you need. ------------->

PSU Connections

Its also important that your PSU has all the connectors that you need. Here is a list of the connectors to look for.

1. PC Main power connector: (usually called P1): Is the connector that goes to the motherboard to provide it with power. The connector has 20 or 24 pins. This connector is the largest of all the connectors. Sometimes the power supply has a 24-pin connector, you can plug it into a motherboard with a 20-pin connector. In cases where the motherboard has a 24-pin connector, some power supplies come with two connectors (one with 20-pin and other with 4-pin) which can be used together to form the 24-pin connector.

2. ATX12V 4-pin power connector: (also called the P4 power connector). A second connector that goes to the motherboard (in addition to the main 24-pin connector) to supply dedicated power for the processor. For high-end motherboards and processors, more power is required, therefore EPS12V has an 8 pin connector.

3.Serial ATA power connectors: a 15-pin connector for components which use SATA power plugs.

4. 4-pin Peripheral power connectors: These are the other, smaller connectors that go to the various disk drives of the computer.

5. 6+2 pin For the purpose of backwards compatibility, some connectors designed for use with PCI Express graphics cards feature this kind of pin configuration. It allows you to connect either a 6-pin card or an 8-pin card by using two separate connection modules wired into the same sheath: one with 6 pins and another with 2 pins.