Modifying the feedback path of an ATX power supply allows you to adjust the voltage of the outputs. The result is a very cheap, efficient, stable supply which can output from 3.1V to around 28V, at up to 3 amps, perhaps more. WARNING: I am not responsible if you electrocute yourself. A computer power supply / ATX power supply is mains operated equipment. It can have voltages of up to 350V across some components when live. Be very careful when working with one. Take all precautions, a shock could be fatal, at the very least it can cause burns and hurts a lot! I used a 1k pot and an old 120W ELENCO power supply. It may well work with different power supplies. In my case, I found I was able to get the rails to vary quite significantly. Your mileage vary vary. 12V: 10.6V - 28.5V 5V: 4.8V - 11.5V 3.3V: 3.1V - 8.5V -12V: -11.1V to -30V 5Vsb: constant 5.06V Future ideas are to add a linear pass transistor voltage regulator on the output - this would drop a few volts but significantly reduce ripple, and to add a microcontroller for features like constant current/constant power/current limited and automatic switching between rails to achieve a full 0-25V range.