So, found some very conflicting answers on the topic.
Bought the card, ATI Radeon HD 3850 AGP. Plugged in, didn't work. Even the fan didn't start. Tried uplugging the extra 6pin power supply, the fan started, but still got no picture.
The card asks for 450W 12V 30A. My old PSU was only 300W, so I went and bought a new one. Trust 520W Pro. Connected everything, and it still don't work, with precisely the same effects.
What could be wrong? I have an onld ATX2.1 motherboard with 20 pins instead of 24 for main power supply. Could this be the problem. I checked my local PC supplier, and he said none of ATX2.2 compliant motherboards have AGP slots, but rather PCIe.
More about :ati 3850 agp usual power supply question
The 20 pin does not matter.
You really can't add up 12+16=28, it's more like you have 23 amps on the 12v rails, which could be your problem. You say you need 30 amps on the 12v rails.
On the OCZ you have 48.33 amps on the 12v rails. 580/12=48.33
The OCZ would be fine for your card.