SFX Bench Power Supply (Variable Voltage)

After looking at many guides on how to convert an ATX power supply to a variable voltage power supply, I decided that most of them were too complicated for a novice to follow and included circuit diagrams that I couldn't decipher. My aim here is to provide instructions that anyone can follow.

Please be aware that you are working with ELECTRICITY here and as such you need to be VERY careful. Make sure you unplug everything before attempting to cut and solder wires. Also be aware that the capacitors inside a power supply can hold high voltages long after the power supply is switched off. Make this thing at your own risk, I will not be held responsible for any accidents. There is actually no need to open the power supply for this build so as long as you unplug it before tinkering, you should be fine. Remember to cut the wires that you don't need and insulate them properly.

Regarding the circuit: It is the simplest way I have found to output a variable voltage of 0-24v (or close en