Combined +12V rails make 432W, So 432 - Whatever my CPU + Motherboard is using = Left over watts for graphic card?
Just a guess there
or I'm completely wrong?
Anything that the CPU and motherboard doesn't use really isn't available for the graphics card and peripherals to use in the case of the Antec Basiq 500 Watt (BP500U).
Each +12V rail is absolutely limited to 20 Amps on each rail.
E.g. if the CPU and motherboard are drawing 132 Watts (11 Amps) from its +12 V rail the unused capacity of 108 Watts (9 Amps) is not available for use by the other +12V rail powering the graphics card and peripherals.
Hardware Secrets review of the Antec Basiq 500 Watt (BP500U) shows that you can't draw more than 20 Amps from each rail. Any attempt to draw more than 20 Amps from either of the +12V rails triggered the over current protection circuit.http://www.hardwaresecrets.com/article/792