[BrianG]

Depends on your PS.

Sometimes, adding a 1A-2A load on the 3.3v line (orange wire), or the 5v line (red wire) can make the feedback regulator work better and bring up the 12v line more.

Sometimes, the PS has a small trim potentiometer than you can tweak the output a bit.

Sometimes, you can "trick" the rail with the feedback line into thinking it is lower than it really is, and the result is that it will boost it accordingly. This requires that a seperate feedback wire be present and is usually the same color as the rail it's monitoring, and connected at the connector (probably to negate v drop due to wire losses). But, determining how to use this wire is too complex for this thread IMO. Here is a hint though: use the feedback wire and a voltage divider of the right values. That's all I'm gonna say on that.