Radeon HD 5770 (Juniper XT) 1GB 128-bit GDDR5 $134.99 to $179.99
Core Clock: 850mhz
Stream Processors: 800
Effective Memory Clock: 4800mhz
Power Consumption at Idle: 18 watts
Power Consumption at Full Load: 108 watts
Recommended is a 450 watt PSU with one 75 watt 6 pin PCI Express connector, but could be run on a quality 400 watt PSU. 600 watt with two 6 pin connectors will be needed for crossfire.
Recommended 37 Amps on 12 volt rail for single card and 50 Amps for crossfire. This card can run on lesser this is just recommended and will be able to run with at least 30 Amps on 12 volt rail.
The above informations are given in the thread:"Power Requirements and Specs For Popular Graphic Cards Guide"
So my question is why have you recommended 37 amp. and minimum 30 amp. on 12 volt rail for this single card while it can easily be run on 25 amp. on 12 volt rail power supply?
Processor i3-540 73watts 73/12= 6.08 amp
Radeon HD 5770 108watts 108/12=9 amp
For Motherboard & other components = 10 amp (maximum)
Total amperes for whole system = 25.08 amp
because not all PSU are equal with many failing to achieve their stated power. the recommendation is to cover the lowest quality of the PSU field. The fact is any quality PSU with 22a on its 12v rail will run the your system with ease. the antec EW 380w is one example that is below 400w in stated power (although easily breaks 400 in peak power) but can power that system with no problem.
*also note the thread in question is SAAIELLO's and represent his views on power recommendation. I'm sure somewhere in his thread he explains how he got to those figures.
Also you are using a fairly low power CPU at 73w while other systems will have 125W CPUs and use even more if OC'd -- so would change the CPU usage from 6 amps to 10.4 amps or more resulting in a new total need of 29.4+ amps even using your numbers ! (and he is making a general recommendation without knowing what CPU is being used so must account for those with higher consumption) - in your case 25amps would work but if using a higher wattage CPU like a PII x4 which uses 125W then 25amps would most likely be unstable !