From Toms review of the 9800GTX Power Consumption And Temperature
As usual, we measured the power supply's consumption for these cards (which means that the consumption of the entire configuration is measured). We also gauged the power-supply losses, which are approximately 18% in the range we're concerned with.
While it requires an additional six-pin power connector, the 9800 GTX' consumption is actually very close to that of the 8800 GTS 512 MB, which is not surprisingly. The figures were comparable in idle state and just slightly higher under load (running Test Drive Unlimited), as its specifications indicated. Officially, Nvidia specifies 156 W for the 9800 GTX as opposed to "< 150 W" for the 8800 GTS 512 MB, and our results confirmed that.
What that means is that a brand-name 350 W power-supply will be enough to feed a system based on this card. We should mention that despite the reduction in memory quantity and the change in engraving depth, the drop in power consumption compared to the previous generation is nothing to write home about - it works out to only 21 W once you correct for the power-supply losses. On the other hand, the performance/watt yield is obviously much higher (by 52%) compared to the Radeon HD 3870 X2, whose consumption we measured with Unreal Tournament III because it was just too underused with Test Drive Unlimited (We measured 235 W, which was actually less than the 8800 GT).
265watts at load for the total test system
In my case it shows about 447(90% tdp & system load) and my system rarely pulls more then 330(i can get it up to about 370 with some real pushing) from the wall(so the DC load is a good 20% lower once you factor in the psu losses)
The system idles around 200 watts, 240-260 folding and 300-330(it varies from game to game) with games added.
Not saying to run out can get a 350 watt psu, but as long as its a good stable psu and sends enough of its power to the 12 volt lines you should be ok. There are many cheap 500 watt psu's out there with as much 12 volt power as a good 350. That may be another reason why EVGA over estimates, then even a cheap psu will run without issues as long as its that far over what is actually needed.
Also overclocking increases power use by allot. To take my Q6600 from 3.0 - 3.6 requires 100(give or take 10 watts) watts extra. Video cards are the same at a point during overclocking the power use jumps a fair bit.
OP- Do you now have a PSU and are trying to figure out if it puts out enough power, or are you trying to figure out what size of PSU to buy? All the discussion is nice, but unless we know what's behind the question, its hard to give a solid answer as to your needs.
I'm usually under the impression when you see what a site recommends, I think they are saying if you have a maximum setup, to where there's nothing left to hookup on the MB/PSU. . o O (but I've been wrong before)
Also related to computer requirements on game boxes:
"Minimum" = count on your fingers frame rates
"Recommended" = "Minimum"
Recommended = Whatever they think
Minimum = Minimum
For example, right off my Oblivion Game box:
1GB RAM / 3Ghz P4 or Equiv CPU / ATI X800 - 6800 NV or higher
512mb RAM / 2ghz P4 or Equiv CPU / 128MB Direct3D compatible video card and DX9
Heh.. they don't say anything about PSU.. garsh darn it.
But what I was saying in my above post, I just remember requirements stated of like NewEgg, to where it depends on how loaded your system is, when it comes down to the PSU. When you run 4-6 HD will cause more Power Draw, then a system with just 1 HD is what I'm saying.
I think things got too complicated for sites on hardware, so they stopped putting them on their (NewEgg/ZipZoom/ect) spec's page when you look at their hardware.