The ATX 24-pin power supply connector is the standard motherboard power connector in computers today.
The connector itself is a Molex 39-01-2240 connector, often called a Molex Mini-fit Jr.
ATX 24-Pin 12V Power Connector Pinout (ATX v2.2)
Below is the complete pinout table for the standard ATX 24-pin 12V power supply connector as of Version 2.2 of the ATX Specification (PDF).
If you're using this pinout table to test power supply voltages, be aware that the voltages must be within ATX specified tolerances.Pinout Reference for ATX 24-pin 12V Power ConnectorsPinNameWire ColorDescription1+3.3VOrange+3.3 VDC2+3.3VOrange+3.3 VDC3COMBlackGround4+5VRed+5 VDC5COMBlackGround6+5VRed+5 VDC7COMBlackGround8PWR_ONGrayPower Good9+5VSBPurple+5 VDC Standby10+12V1Yellow+12 VDC11+12V1Yellow+12 VDC12+3.3VOrange+3.3 VDC13+3.3VOrange+3.3 VDC14-12VBlue-12 VDC15COMBlackGround16PS_ON#GreenPower Supply On17COMBlackGround18COMBlackGround19COMBlackGround20NCWhite-5 VDC (Optional - Removed in ATX12V v2.01)21+5VRed+5 VDC22+5VRed+5 VDC23+5VRed+5 VDC24COMBlackGround
The pinouts for the 15-pin SATA Power Connector, 4-pin Peripheral Power Connector, 4-pin Floppy Drive Power Connector, and for other ATX power supply connectors can be seen in our ATX Power Supply Pinout Tables list.
More Information on the ATX 24-Pin 12V PSU Connector
The ATX 24-pin 12V power supply connector can only be plugged in while pointing a specific direction on the motherboard. If you look carefully at the following illustration, you can see that the pins take a unique shape, a shape which the motherboard matches in only one direction.Ach5 / Alex Dos Diaz
The original ATX standard supported a 20-pin connector with a very similar pinout as the 24-pin connector but with pins 11, 12, 23, and 24 omitted. This means that the newer 24-pin power supply is useful for motherboards that require more power, and therefore eliminates the need for ATX 12V power supplies to provide an auxiliary power cable (although some still may).1:20
How to Manually Test a Power Supply With a Multimeter
24-Pin & 20-Pin Compatibility
The additional four pins are usually detachable (like you can probably see in the lower part of the image above), allowing it to be used on a 20-pin motherboard connection. The extra block of pins simply hangs over the motherboard connector—they don't plug into another slot. Some motherboards allow the reverse: to use the older 20-pin power supply cable on a 24-pin motherboard connection.
If you need to use a 24-pin power supply connector on a motherboard that only accepts a 20-pin cable, there are a number of online retailers where you can purchase a 24-pin to 20-pin adapter, like this StarTech adapter from Amazon. Though the motherboard appears to accept all 24 pins using this type of adapter, it still, of course, means that the additional four pins go unused.