Converting a Mac Power Supply to ATX motherboard its no so hard to do. On the Picture above there is a ATX power supply on the left and a Mac on the right. The connectors on the power supply are different for the 2 computers but the cables are color coded equally.

Step 1:

Here is the diagram for the 20 pin & 24 pin Connector, most computers now use 24 pin connector.

Step 2: Diagrams of Pin Out

Here is the diagrams of the pin out for the ATX Motherboard.

Step 3: Welding Process

On the ATX power supply you have to cut the cables close to the PWS Mother Board.

On the Mac PWS you will cut the end of the connector.

Now match the cables by color.

Yellow = 12VDC

Red = 5 VDC

Orange = 3.3 VDC

Black = Ground

White = 24 VDC (Mac)

Step 4: Test

Testing the Power Supply with an old ATX Motherboard.

Step 5: Final Result

On the Mac PWS you will find a White cable = 24 VDC you don't need to use this cable for ATX Motherboard.
Use heat shrink on the cables that you are welding to prevent a short circuit.
Do not use electrical tape as it may fall off and can cause a short and burn your PC or cause a fire.
Have in mind that the Mac PWS only provide 460 Watt.