Computer power supply units (PSU) deliver the power to the PC hardware via a number of cables with connectors. The generic specifications for various PSU form factors intended for use with desktop systems are defined in Intel's design guides, which are periodically revised. The latest standard is Design Guide rev.1.1 released on March 2007, which combines the requirements for CFX12V, LFX12V, ATX12V, SFX12V, TFX12V and FLEX ATX.
Standard ATX-style power supplies for desktop PCs typically have the main power connector and additional 12V connectors, as well as peripheral, floppy drive, serial ATA, and PCI Express® connectors. To support 75W PCI Express® requirements, in the new ATX systems the old 20-pin main connector has been replaced by a 24-pin connector. Accordingly, different ATX-style smps may use different number of power supply wires: see the diagram for pinouts of the old and new power connectors. The colors in this chart represent recommended colors of the wires in the PSU cables. The diagrams reflect the front (pin-side) view. The colors are shown here just for reference: you need to look from the back of the connector to see the colored wires. Main connector uses Molex Housing Mini-Fit Jr. P/N# 39-01-2240 or equivalent (old part number 5557-24R), contacts: Molex 44476-1112 or equivalent, mating motherboard connector is Molex 44206-0007. The old 20-pin ATX connector was Molex 39-01-2200 or equivalent, mating motherboard part was Molex 39-29-9202. Under certain conditions new PSU can still be used in an old PC and vise versa- see our guide on connecting 20-pin PSU to 24-pin motherboard.
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