How to check the power supply (SMPS) of a computer.

To check the power supply without the motherboard- Short the green and any black wire. The fan should start rotating.

Technical explaination- Attach a fan on one of the 4 pin molex. On the 20 or 24 pin ATX power connector, short the pin that has the GREEN wire with any adjacent pin that has the BLACK wire. Attched fan and PSU fan should spin. You can test the +3.3V and +5V rails with a multimeter. Pins with the Orange wire carry +3.3V while RED carry +5V.

Power Supply Connectors

The board has the following power supply connectors: (4 pin connector)
1 Ground
2 Ground
3 +12 V
4 +12 V

Main Power
1 +3.3 V
2 +3.3 V
3 Ground
4 +5 V
5 Ground
6 +5 V
7 Ground
8 PWRGD (Power Good)
9 +5 V (Standby)
10 +12 V
11 +12 V (note)
12 2 x 12 connector detect
13 +3.3 V
14 -12 V
15 Ground
16 PS-ON# (power supply remote on/off)
17 Ground
18 Ground
19 Ground
20 No connect
21 +5 V
22 +5 V
23 +5 V (Note)
24 Ground (Note)

Note- i think these are not connected when using a 20 pin connector inside a 24 pin.

Note: When using a 2 x 10 power supply cable, this pin will be unconnected.