The "SLI Ready" logo on Power Supply boxes may make you think it is certified to run SLI, but that may not be so.
You may find yourself in the same shoes as I am, when you are trying to diagnose motherboard problems and the MB techie asks how many amps your power supply can handle for 5v, 3.5v, etc. and then tells you it isn't big enough for the SLI video card you bought. "But, it said it was 'SLI Ready'" "Sorry, but it's not."
So, where do you go to find out what Power Supply to buy? The Power Supply people don't tell you. The motherboard people say to ask nVidia. nVidia says they don't provide technical information for video cards, they just make the chip that goes in them. The video card people won't tell you. And from each of these sources I have found some that did not know. My motherboard supplier techie said, "Here are the amps we'd like to see ..."
Now, many are going to say, "Why didn't you look at _____ site?" Well, I never found _____ site, that's why.
But eventually I did find this site; note that it's not nVidia.com: slizone.com/object/slizone_build_psu.html
There, notice that there is a different selector for GTX, GTX, and other configurations.
Oh, you say, I'll just send my power supply back if I find this out later. Oh, no you won't. The supplier has this little tag that says they will only take it back if it is defective, that you are under the manufacturer's warranty, which does you a whole lot of good if you bought the wrong power supply! You now own an EBay item.
I concluded that I was stuck with my power supply and replaced it while I am chasing down motherboard problems in my new system. In so doing, the new power supply died. Yippee! I sent it back as defective and was in an excellent position to ask for an upgrade, which I got. The original power supply was 600 watts, the new one is 850 watts. In looking back on how I went about it, there is no way I would have found the right site to look for the right product.
One big problem with the SLIzone site is that it appears to be out of date. Here are all these hot cards coming out and the power supply people are racing to put big enough products out there and they have the dreaded "SLI Certification Pending" status, which means you don't know if it is or if it isn't. So, like me, you buy it anyway, because by now you know what kind of specs you need. Hope it works. Thanks a lot, nVidia, for not finishing the project!
So, what happens if you don't buy a big enough power supply? One engineer explained that you should be able to boot up all right. But when your video card starts pumping, the power supply won't be able to keep up and will then shut down. Supposedly, they build them so they won't smoke.
So what's needed? First, the "SLI Ready" logo ought to say which SLI card the product is certified for. That is a MUST! Secondly, since the SLIzone site is running behind, they ought to provide the specs for certification so we can see what the vendor claims for the product before they accomplish certification. Now, nVidia is probably saying I don't know what I'm talking about, and they're right! It's their job, not mine. But they didn't do their job. Why don't they come out with a working plan? That plan ought to meet the problems I've described in this paper.
Right?
John

"John"

err no....cos the SLI logo means it can run SLI which is correct...I had 2 x leadtek 8800gts card in SLI config and my PSU (Enermax Liberty 500watt) ran them easily, then I upgraded to two Gainward 8800GTX cards and it would run in SLI even though the PSU stated it was SLI but the 8800GTX cards have 2 PCI-E power adaptors per card so I needed a new PSU...simple really Scotty©

"Scotty©"

sorry should have read that it wouldn't run in SLI mode for the 8800GTX and the PSU I bought was the Enermax 720watt which will run the 8800GTX no probs at all Scotty©

"Scotty©"

This site does a great review of some power supplies out their.
hardocp.com/
Tom