So 7570 max needs are 44 wats and 20 amps and 400W psu.
I know that wattage use differ in PC parts (better CPU = bigger wattage)
But what about that 20 amps? Does that mean that you need 20 amps on 12V rail to make GPU work?
I can't connect formula with informations i have.
I will be happy to see some answers. TNX
The formula isn't really used as part of their recommendations. The 44W means the gpu itself will draw 44/12 = 3.67A from the 12v rail (assuming their 44w is accurate; it seems reasonable).
However, to recommend a power supply, it must account for the rest of the system, so they have to make up numbers for the rest of the system, and arrive at a 400W PSU rating (for the whole PSU) with at least 20A (240W) from the 12V supply.
A processor can consume as much as 125W depending on brand and chip (I believe the CPU draws from 12v supply), and HDDs and Optical drives will also consume 12V power to some degree for spinning motors (lets say 75W from 12v), so add in a 44w GPU, and you've got a 244w requirement on your 12v rail, approx 20A.