Changes to ATX standard were made to support 75 watt PCI Express requirements. New ATX v 2.x uses new connector, but most motherboards nowdays allow to use an old ATX v 1.x power supply with 20 pin connector - it connects to 24 pin motherboard receptacle.
| Pin | Name | Color | Description | |
|---|---|---|---|---|
| 1 | 3.3V | Orange | +3.3 VDC | |
| 2 | 3.3V | Orange | +3.3 VDC | |
| 3 | COM | Black | Ground | |
| 4 | 5V | Red | +5 VDC | |
| 5 | COM | Black | Ground | |
| 6 | 5V | Red | +5 VDC | |
| 7 | COM | Black | Ground | |
| 8 | PWR_OK | Gray | Power Ok is a status signal generated by the power supply to notify the computer that the DC operating voltages are within the ranges required for proper computer operation (+5 VDC when power is Ok) | |
| 9 | 5VSB | Purple | +5 VDC Standby Voltage (max 10mA) | |
| 10 | 12V | Yellow | +12 VDC | |
| 11 | 12V | Yellow | +12 VDC | |
| 12 | 3.3V | Orange | +3.3 VDC | |
| 13 | 3.3V | Orange | +3.3 VDC | |
| 14 | -12V | Blue | -12 VDC | |
| 15 | COM | Black | Ground | |
| 16 | /PS_ON | Green | Power Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF. | |
| 17 | COM | Black | Ground | |
| 18 | COM | Black | Ground | |
| 19 | COM | Black | Ground | |
| 20 | -5V | White | -5 VDC (this is optional on newer ATX-2 supplies, it is for use with older AT class expansion cards and can be omitted on newer units) | |
| 21 | +5V | Red | +5 VDC | |
| 22 | +5V | Red | +5 VDC | |
| 23 | +5V | Red | +5 VDC | |
| 24 | COM | Black | Ground |
