PC Power Supply Mod.

[BrianG]

Chances are that loading one of the 5v or 3.3v lines will help. Unfortunately, since all supplies are different, it could be the 3.3v line OR the 5v line, no way to tell until you experiment unless you want to reverse-engineer the circuit to determine the current sampling coil. So, it's just easier to temporarily hook up your resistor to each rail, and load whichever rail produces the most benefit the 12v line. Usually, drawing around 1A from either of these rails is enough to stabilize the 12v line, which means 5 ohms for the 5v line and ~3 ohms for the 3.3v line.

BTW: Even at 1A, the resistor should be mounted on a heatsink somewhere.

Also make sure the resistor power rating is sufficient. So, let's say you find that you need to draw 1.5A from the 5v line for sufficient 12v stability; that's 3.33 ohms and 7.5w. You want a resistor that has at least double the power rating of what you calculated.