ATX specification includes not only Power Supply Unit, but also interface to case and motherboard. In addition to the old AT standard, ATX 2.0 has one extra voltage line available (+3.3V), a connector chain-lined to the single 20-pin and a power-on wire that allows Software to turn off the PSU.
Several units (on hand) show pin-12 as Brown (not Blue), pin-18 as Blue (not White), and pin-8 as White (not Gray). Pin 9 (standby) goes from 0 to 5V and pin 14 goes from 0 to 3.7 when PSU switch is turned on. Shorting pin 14 (/PS_ON) to GND (COM) causes power supply to switch ON and PWR_OK to change to +5V.
| 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) 500mA or more typical |
|
| 10 | 12V | Yellow | +12 VDC | |
| 11 | 3.3V | Orange | +3.3 VDC | |
| 12 | -12V | Blue | -12 VDC | |
| 13 | COM | Black | Ground | |
| 14 | /PS_ON | Green | Power Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF. | |
| 15 | COM | Black | Ground | |
| 16 | COM | Black | Ground | |
| 17 | COM | Black | Ground | |
| 18 | -5V | White | -5 VDC (2002 v1.2 made optional, 2004 v2.01 removed from specification) | |
| 19 | 5V | Red | +5 VDC | |
| 20 | 5V | Red | +5 VDC |
Activating /PS_ON turns on the power supply.
