This is a very simple to build and very powerful power supply for basic electronics, but for a newbie can seem confusing if he tries to make the conversion on its own. The power supplies used in PC’s have useful output voltages like 5V, 12V, 3.3V and even some negative outputs -5,-12V. While the positive outputs can handle significant current, the negative rails tolerate just a few hundred milliamps.
I recently needed about 12 and 10A, since my bench supply can handle only 2A I used an old 250W PC source, on the label was 12V/15A but the voltage dropped to 10V at 5A load, so don’t be surprised if you encounter similar “effects”.
Don’t forget the dummy load on the 5V rail, to be honest I never used it and the supply worked just fine, but to avoid any problems load the output with 0.5A. In lack of power resistor use any 12V light bulb, it will do just fine.
ATX power to bench power: [link]