Crap.. I was half-asleep when I wrote that. My PM was to shambler, not scalliano. Sorry about the confusion!
I don't think any nVidia boards require a 500watt PSU. I think a 400 is recommended or something like that. Now if you SLI two 6800Ultras... that's another story. I'd really do some serious research on the wattage requirements if anyone's insane enough to do that (and has that much money to throw away). What's more important than raw wattage is maximum deliverable Amperes on each rail. If you have a 425 watt PSU that can only put out 10 amps on the 12 volt rail, you might as well use it as a rifle target. Higher amps per rail is always better, but how it's divided is also important. Having all of it dumped to the 12 volt rail would be great for peripherals, but lousy for the CPU which needs it on the 3.3. When comparing brands and models within the same wattage ratings. Here's an example of what you might see:
DC OP/Load Max. Min.
+5V 44A 11A
+12V 20A 5A
+3.3V 38A 0A
-5V 2A 0A
-12V 1A 0A
+5VSB 2.2A 0A
Max Continous DC output power shall not exceed 431W.
Max output combined on +5v & +3.3V shall not exceed 220W.
These are the specs off my power supply. Note the max output is 431W, even though it's a 460Watt PSU. There's a reason for this, and it's not false advertising (though it would seem so) and
every power supply manufacturer on the market does this. What you want to do is look at your amps per rail and combined wattage and match them to your needs.
Some PSU's have dual 12 volt rails, some have a single 12 volt rail. Some argue dual-rail PSU's are better because the current load is split between the mainboard connector and the peripheral connectors, reducing electrical noise and maintaining a cleaner power signal to the mainboard/CPU by isolating peripherals on the other rail. I've also heard it argued that dual-rail PSU's exist because it's cheaper to manufacture a two-rail PSU than a single-rail, high-wattage PSU. A single-rail's advantage is that it allows all devices to draw from a pooled supply. Either way, the best power supplies out there will have a very large current capacity on all the important voltage levels (5v, 12v, 3.3v) and will have a lot of open space for airflow. PSU's with larger fans are preferred, and dual-fan PSU's are nice not in that airflow is really increased but rather that if one fan stops the other will continue to ventilate the unit. Of course there are other bells and whistles to consider, but they're useless unless the unit can keep up with current load of the devices. Stability should always be the number one consideration of any power supply, with "nifty features" and price coming in well after that factor. You can have $1000 in quality components and skimp on a $20 power supply trying to feed it and you'll sit there wondering why your system keeps crashing all the time. It's like towing a 53 foot long semi trailer with a Yugo, why would you do that? Why do the same with your PC?
Most power supplies that come with cases are really low-end like mecha said. I've seen some Enermax cases that come with Enermax power supplies (big surprise, considering they made the case), and there are some Antec ones out there I believe but those are the
only bundled ones I've seen that are any good. Enermax is the best manufacturer from what I've seen, with Antec running a very close second. Now I've seen articles rating Antec a lot higher than Enermax based solely on combined wattage output. I have a problem with that, as combined output should
not be the only factor in determining quality. I'm using a 460 watt Enermax in my system, and my voltage levels have
zero fluctuation when viewed in realtime on my monitoring software, even if I kick all of my fans to full throttle, whereas I've seen the most expensive Antec models on the market that have the same ripple as a 400Watt CodeGen that came with my old Noblesse case. One of those fans of mine is a 119CFM Tornado that draws 12 watts of power, as well as three additional 50CFM Sunons and various other fans and blowers. This was NOT a cheap power supply, I paid $100 for it new several years ago. However, I've only paid for it once, and I have no stability problems whatsoever (so long as I don't do something stupid like overclock my video card but that's not a power issue). Stability is not something that's achieved just through high wattage/amperage ratings. Component grade really comes into play here. If you've ever seen or built a bridge rectifier you'll know what I'm talking about when I use the term "ripple". The less ripple the better, and to get a really clean DC signal the rectifier has to have beefy filter capacitors on it. The bigger the better when it comes to filter caps. For those who don't know what a rectifier is, it's what converts AC from the wall into DC for the computer to actually use. The bridge rectifier is the heart of
any power supply. Basically you want a beefy transformer coil and beefy caps on the rectifier. That's what will give you clean, stable power flow.
Another thing to consider is the whole "how much do you
really need" or "can you have too much power" arguments. The short answer is "No". Remember that the closer you run an electrical device to its maximum, the more it's going to be stressed and the more it's going to heat up. You always want some breathing room. It's no different from redlining an engine. You can baby a car and make it last, or burn it up in a year's time. Same with a power supply. If you can maintain a 20% or better ceiling from your actual load you're in good shape, and the power supply should be adequate for your needs. If you try to max out an underpowered supply you can expect to run into the problems mecha did, along with such fun things as random reboots, boot failures, blue screens... need I go on?
Now in Europe the branding is different, so some stuff may not be available there. I know when I was putting spec recommendations together for shambler his preferred vendor doesn't sell a lot of stuff you can find in the US, and there's a lot of stuff there that doesn't exist in the US. It makes it a trickier game recommending the best components![/color]