NOTE: This testing applies only to the standard ATX PSU, it does not apply to proprietary PSU’s (ie: older Dell’s ) which use a different pinout arrangement for their ATX connectors (non-standard).
20 and 24-Pin Connectors: The 24-Pin connector has an additional 4 pins attached to one end of the connector. The top 20-Pin section is electrically identical to the original 20-Pin ATX connector. Due to the additional connections the numbering sequence changes, so if you have a 24-Pin connection then make that adjustment when comparing with a 20-pin
+3.3v pins 1, 2, 11 (Orange wires)
+5V pins 4, 6, 19, 20, (Red wires)
+12V pin 10 (Yellow wires)
-5V pin 18
-12V pin 12