I am planning a new PC with AMD PII 965, 4GB DDR3, single 5770 1GB, 1TB 7200.12 HDD and a DVD RW. How big the PSU should be?
I am a bit confused by recommendations and review result. In Tom's review, (http://www.tomshardware.com/reviews/radeon-hd-5770,2446...) full load power consumption is only 207W, so a 400W PSU should be enough. but "Power Requirements and Specs For Popular Graphic Cards Guide " in this forum says
" 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. "
37 Amps on 12 volt translates to 444W, but 5770 max load power is 108W by specification which should be less than 10A on 12V. I am really confused
A 400W PSU like the CORSAIR CX400 400W is more than enough to power your computer. Nowadays the most power-hungry component in a computer are the cpu and the graphic card (both take the power from the +12V output). But if you have an OC power-hungry cpu, a lot of HDs, a case full of fans, liquid refrigeration, etc, the wattage that you will need is increased from those theorical 210W. That's why the recommended wattage is higher. The manufacturer considers a heavy load configuration.
On the other hand, you have to take in mind that the PSU usually achieves its highest efficiency when delivering between 40% and 60% of its maximum capacity. A more efficient PSU brings two advantages. First, a lower electricity bill. The second advantage is less heat being produced (the PSU will be quieter too because it doesn´t need to increase the speed of the fan). So, if the difference in the price is not high, it's interesting to choose a PSU with 450W although you only will use the 60% of the available power. Anyway, in your case, the Corsair CX400 is fine.
The Nexus 430 is the quietest psu ever reviewed by SPCR and an Editor's Choice.
It is a high quality unit and has 80% efficiency. http://www.silentpcreview.com/Nexus_Value_430
That being said i agree with the other posters that the cheaper Corsair's will do the job just fine.
Chances are other fans in your rig will be louder then your psu's fan.
It looks like 400 watts is enough for your rig.. But its never harmful in getting a little extra (especially when it comes to power).. Unplanned hardware upgrades and stuff like overclocking can keep you wanting for more and thus need to be taken into consideration while getting a PSU..