Originally posted by: Tostada
1000W PSUs are mostly made because the market exists. That is, there are clueless kids out there with a lot of cash to spend, and they think a 1000W PSU is a good idea for some reason.
I can appreciate the KISS approach with any build, but a 1kW really isn't such a bad idea.
Fact is that UL and Intel spec state that more than 240VA on a single DC output is "unsafe." But 20A per 12V rail is not enough unless you have more than two 12V rails.
It's a fact that ATX12V and SSI specs require the CPU gets it's own rail, so you're left with a single 240VA rail for EVERYTHING but the CPU unless you have more than two 12V rails.
It's a fact that Crossfire X1900's or SLI'd 7800's or 7900 GTX's need more than just a couple 20A rails. In fact unless there's a 20A rail or a pair of rails dedicated for the PCI-e power connectors, a fully loaded system (say four hard drives, two opticals... the kind of system that coincides with a pair of X1900's or 7900 GTX's. In other words: More money than brains.) will FAIL during heavy use (gaming with all eye candy turned on, for example.)
It's also a fact that efficiency of a power supply appears as a bell curve with the best efficiency in the upper 60-70% of the power supply's output capability. So if you use an "undersized" PSU that's sufficient, but used to it's maximum capability, you're not at the worst point of efficiency, but not at the best. Remember the buzz words used in "highly efficient" power supplies are "maximum efficiency" or "typical efficiency." The rating that really matters is "minimum efficiency" but too many manufacturers are scared to use it.
Also, de-rating curves are also a fact of life. The hotter a PSU gets, the less power it puts out. Add a couple 7900GTX's in there, which can easily work as make-shift Sterno burners, and your ambient temps are way over 50C. Of course, some PSU's have de-rating curves better than others. Some are 1W per 2C, some are 2W de-rate per 2C. But nobody publishes de-rating curves, so who knows how that PSU performs under stress.
The S12-600 is a GREAT PSU. No doubt. But the fact of the matter is, it can not hold up in a PC with a pair of X1900's, 7800GTX's or 7900GTX's. Been there, done that. It doesn't work... not and at least allow you to have all of the eye candy turned on. And if you can't do that, what's the point of having the Crossfire or SLI? And to show that I'm not being biased: An X-Finity 600W or X2 550W can't cut it either.
Now I'm not saying you NEED a 1kW power supply. But that "wattage" rating is so deceptive.. I mean... you can't even go by it because that number doesn't allow the user to take into consideration operating temperature, de-rating curve, minimum efficiency, etc.
Fact: Even an FSP600 will work better than a Seasonic S12-600W in a high end rig. What?! Only a 600W? But how? Because the FSP has FOUR independent 12V rails with the PCI-e's having their own 12V rails, it has a better de-rating curve and is rated at a higher operating temperature than most any other PSU. In other words: It's a better power supply. Nothing to be ashamed of, but it's a better power supply. And if Enermax or PC Power and Cooling have to make a 1kW PSU to compete with it, who are you and I to say, "you don't need a 1kW power supply" if THAT is what it's going to take to get a PSU from those particular manufacturers that's going to work in a higher end gaming rig.
Seasonic is going to have to pony up with an 800W (using their current specs for operating temperature, derating curve, etc.) in order to compete in that league. But when they get there, I'm sure it'll be a fantastic product.