There's usually not much money to be saved with less than a 650 watter as newegg for example typically has specials on top quality ones like the EA-650 for as little as $50...also PSU's run at peak efficiancy at about 50% load so there's no downside to oversizing and it gives you room for upgrades.
Unfortunately, with pent up demand for the new SB MoBos / CPU's resulting in lotta new builds, newegg has put the brakes on these deals atm
First comes need wherin you need to match the PSU as per your conponents requirement.. A 650W PSU (preferably) from a good brand is moRe than capable enough to handle any single GPU configuration.. Then comes the quality of the PSU which in most cases can be determined from The brand.. Efficiency helps determine power ouTput and bills.. Thus, higher the efficiency the bEtter it is.. Modularity helps somewhat with cable management.. However, if you may need as much cables as possible (4+ hard drives, couple of video cards, multiple optical drives etc.), you may as well go for a non modular unit which tend to be a little less in price compared to their modular counterparts..
In summary, buy power supplies where the maximum capacity is on the +12 V outputs and not on the +5 V/+ 3.3 V lines.
Finally you will need to know how much power your PC will really consume before picking a power supply. There are several calculators on the internet that can help you out with this; we recommend this one.
We also recommend you to choose a power supply that will be working between 40% and 60% of its maximum capacity. There are two reasons for that. First, efficiency, subject that we will explain next. Second, you will have headroom for future upgrades. So get the result obtained from the calculator and multiply it by 2. This is the power supply wattage we recommend you to buy (you will be surprised that most systems will require a power supply with less than 450 W, even with our adjustment).
You didnt read everything did you?
i summrize it i find articales , i learned about 80plus, peak, peak ,continous ,noise , generic
now i understand i can go on 400w-450w (with adding future video card) but in the calculate sites i get much than i thought