What are a PSU's normal values in the box?

[Hoshi_Reed]

If a PSU is plugged in the outlet and the green/black wires shorted to turn it on (no connectors to the MB or anything) are the values:
12.9, 3.8, 5.9 still too high?

When connected to the motherboard the bios voltage are much lower, around 12.2, 3.46, 5.1
and PCWizard 2010 gives an even lower reading - 11.93, 3.41 and 5.14

I'm too afraid to test it while connected to the motherboard (just in case I touch something I shouldn't with my meter probe and fry)

 

[Route44]

In order to test a power supply correctly the psu must be connected to the motherboard and running. You are not going to fry anything. Are you using a digital multimeter?

It works in percentage tolerances.

The bare minimum is 5% and most good manufacturers go to 3%. And the really good supplies are tighter than 3%.

so for 5% they have to be between:
12v: 11.4v <--> 12.6v -- though 12.6 is not something I would want to see
5v: 4.75v <--> 5.25v
3.3v: 3.135v <--> 3.465v

And for 3% they can be between:
12v: 11.64v <--> 12.36v
5v: 4.85v <--> 5.15v
3.3v: 3.201v <--> 3.399v

* Your 3.3v is the one that stands out as pushing the tolerance levels.