Hacking an ATX power supply to work with RAMPS 1.4 is quite dangerous… Power supplies which can give you the Amps are rare.
Here’s a nifty solution. A simple ATX power to RAMPS intermediate board.
Plug in an ATX 24 Pin power connector and two of the 4 pin molex power connectors (preferably from a dual rail supply). Wire them up to the output molex with the bottom pin of the output molex supplying the power for the heated bed.
The 5V and PS-ON pins can be wired to the RAMPS 1.4 to offer auto-power on (if like me you’re making a bluetoothy remote printer).
Download the Fritzing sketch here.
With this board, next time you blow up an ATX power supply, you don’t have to go through the process of hacking another one… Which increases the chances of electrocution each time…