The topic of the 80 plus certification in relation to efficiency is another thing to think about. Just because it says 500w on the box, doesn't necessarily mean you will be able to draw all 500 watts, especially on cheaper units.
It's the rails man, read the BLOODY SPECS OF THE PSU, I get so bloody worked up about shitty PSUs and people buying and recommending all kinds of shit, yes SHIT to people without actually taking the time to just read a little bit about how switched-mode power supplies work.
Power supplies are designed around 40% greater than the calculated system power consumption. Power supplies label their total power output, and label how this is determined by the amperage limits for each of the voltages supplied. Some power supplies have no-overload protection.The system power consumption is a sum of the power ratings for all of the components of the computer system that draw on the power supply. For certain graphics cards, the PSU's 12 V rating is crucial. If the total 12 V rating on the power supply is higher than the suggested rating of the card, then that power supply may fully serve the card if any other 12 V system components are taken into account. The manufacturers of these computer system components, especially graphics cards, tend to over-rate their power requirements, to minimize support issues due to too low of a power supply. Although a power supply with a larger than needed power rating will have an extra margin of safety against overloading, such a unit is often less efficient and wastes more electricity at lower loads than a more appropriately sized unit. For example, a 900-watt power supply with the 80 Plus Silver efficiency rating (which means that such a power supply is designed to be at least 85-percent efficient for loads above 180 W) may only be 73% efficient when the load is lower than 100 W, which is a typical idle power for a desktop computer. Thus, for a 100 W load, losses for this supply would be 37 W; if the same power supply was put under a 450 W load, for which the supply's efficiency peaks at 89%, the loss would be only 56 W despite supplying 4.5 times the useful power. A power supply that is self-certified by its manufacturer will claim output ratings that may be double or more than what is actually provided. Most "500 watt" PC PSUs can't actually deliver 500 watts constantly for any length of time.
That's often OK, because it's hard to create a computer that loads up the different rails of a power supply in the right proportions to add up to the thing's total official power rating, anyway. If the degree of spec inflation is not high, then it won't actually matter any more than the fact that your car's speedometer goes 50 km/h higher than the vehicle can actually manage.
But suppose you're a bargain hunter armed with the knowledge that your new gaming box will have an actual peak power draw of, say, 350 watts, well within the capacity of any decent "500W" PSU. You may be dismayed to discover that the "500W" PSU you bought from a marvelously cheap dealer will barely get your PC to a Windows desktop, much less let you run a 3D game. The very cheapest high-rated PSUs, mind you, are complete junk. It's actually possible to find "ranges" of PSUs that have different ratings and different prices, but are all exactly the same inside. Sometimes they come with sheets of rating stickers which the retailers can apply as needed. That certainly makes inventory management easier. Transient super-high current draw from one component can cause the 12V output that component's running from to temporarily dip well below spec, and it's theoretically beneficial to split the computer up into two or more zones, to limit the number of other components that such a glitch will affect. Prime example is a 1200W Thermaltake unit that has no fewer than four 12V outputs, two rated at 20 amps and two at 36A (...and yes, that adds up to 1344 watts in total before you even take the other rails of this "1200W" PSU into account, which tells you that you definitely can't fully load even all of the 12V rails at once).
It's perfectly possible for a PSU manufacturer to just ignore ATX v2, though, and run all of the PSU's 12V outputs in parallel from one super-beefy regulator circuit. In practice, that's likely to work just as well, as long as the one monster circuit isn't very optimistically specified, as they often are in simpler PSUs.
The only real problem with the one-12V-rail idea for most purposes is that a PSU that can deliver several hundred watts through one wire will happily do so if that wire gets shorted to ground. A single-12V-rail version of a "1200W" PSU might be able to deliver a whole kilowatt at 12V, which could cause something quite impressive to happen if you slammed the case closed on a drive power cable.
It's quite easy to hang a multimeter off a drive power connector while the system boots to see if there's a horrible sag, by the way. It's possible that all of your hard drives or fans spinning up at once may now be overloading one of the PSU's outputs.
Realistically, of course, it's virtually impossible to get anything that uses an ATX-type PSU to consume 1.2 kilowatts, let alone 1.5.
Thermaltake put "Quad GPU Ready" on the 1.2kW Toughpower's box, and they're not lying, but there's not a lot of point buying a power supply today for the theoretical 600-watt showpiece graphics systems of tomorrow
here, go read from a tech blog
http://www.anandtech.com/show/2624/3
Nah I am starting to feel like perhaps spending that extra money on a decent PSU can probably help me in the long run. Rather that then have something possibly go wrong with an el Cheapo.
