Originally Posted by KillerBug
The 3.3V is a signal from the PS3 to the power supply to signal it to turn on...it is not a supply voltage and it is low current.
A note on 12V rails...you don't want to mix them on a single device. You can run the bluray and the mainboard of different 12V rails, but you don't want to run all of your 12V rails together to a single point like the 12V pin of the mainboard...if you could do this, the PSU would come like that. Most quality PSUs have a single 12V rail anyway...you mostly only get more rails if the PSU is low quality or if it is very high current (like those 1200W monsters).
the 3.3v is not needed as it's only for the ps3 psu..
as long as you bridge the pc psu you won't need to mess with it.