I see many questions about whether a PSU is enough to drive a video card. I get the feeling that people generally think video cards use much more power than they actually do. Let's review some basic facts:
A PCI-E 1.x motherboard delivers a maximum of 75W to each PCI-E 1.x slot.
A PCI-E 2.0 motherboard delivers a maximum of 150W to each PCI-E 2.0 slot.
Each 6-pin PCI-E power connector delivers a maximum of 75W to the video card.
Each 8-pin PCI-E power connector delivers a maximum of 150W to the video card.
Watts = Volts x amps
Video cards are run on the 12v rail, so for our purposes, Amps = Watts / 12
Therefore:
The most a video card that requires no power connectors can pull under any circumstances is 150W, or 12.5 amps.
The most a video card that requires one 6-pin PCI-E power connector can pull under any circumstances is 225W, or 18.75 amps.
The most a video card that requires two 6-pin PCI-E power connectors can pull under any circumstances is 300W, or 25 amps.
The most a video card that requires one 6-pin PCI-E power connector and one 8-pin PCI-E power connector can pull under any circumstances is 375W, or 31.25 amps.
Most video cards actually pull far, far less than these maximum amounts. Note that video card makers must still assume that the user might want to run the card on a PCI-E 1.x motherboard, so they cannot assume that extra 75W from the PCI-E 2.0 slot will be there.
The above statements are fact, and not open to debate. When you ask how much a specific video card actually pulls, it gets much more debatable, because as far as I know, nVidia and ATi don't officially state how much wattage their reference card designs pull. You have to search around and find articles where reviewers have deduced how much power the video card consumes.
Below I list some video cards and the amount of wattage that reviewers say they use under full load. I list standard reference clock speeds only; overclocked cards will use more power (sometimes much more) and there are too many of those to list each one. Wattages listed are for the card only, not for the entire system.
Disclaimer: This list is only as trustworthy as the reviewers quoted. Sometimes the reviewers agree (see the 4850 entries), sometimes they disagree (note the GTX260 192 entries). I didn't make any of these measurements, nor would I know how to. Sources are listed in parenthesis. I may add more as I find them or have them pointed out to me.
nVidia GTX280: 178W, or 14.8 amps (XBitLabs)
nVidia GTX260 (192 stream processors): 122W, or 10.2 amps. (SPCR)
nVidia GTX260 (192 stream processors): 136W, or 11.3 amps (XBitLabs)
nVidia 9800GX2: 182W, or 15.2 amps (XBitLabs)
nVidia 9800GTX+ (two 6-pin PCI-E power connectors): 114W, or 9.5 amps (XBitLabs)
nVidia 9800GTX+ (one 6-pin PCI-E power connector): 80W, or 6.7 amps (XBitLabs)
nVidia 9800GTX: 108W, or 9 amps (XBitLabs)
nVidia 9800GT: 83W, or 6.9 amps (XBitLabs)
nVidia 8800GT: 78W, or 6.5 amps (XBitLabs)
nVidia 9600GT: 60W, or 5 amps (XBitLabs)
nVidia 8800GTS 512MB: 99W, or 8.25 amps (XBitLabs)
nVidia 8600GTS: 47W, or 3.9 amps
ATi 4870X2: 264W, or 22 amps (XBitLabs)
ATi 4870: 130W, or 10.8 amps (XBitLabs)
ATi 4850: 101W, or 8.4 amps (SPCR) (XBitLabs)
ATi 4830: 85W, or 7.1 amps (XBitLabs)
ATi 3870X2: 171W, or 14.25 amps (XBitLabs)
ATi 3870: 81W, or 6.75 amps (XBitLabs)
ATi 3850: 63W, or 5.25 amps (XBitLabs)
ATi 4670: 47W, or 3.9 amps (XBitLabs)
ATi 2900xt: 161W, or 13.4 amps (XBitLabs)
ATi 2600xt: 49W, or 4.1 amps (XBitLabs)
ATi x1950xtx: 110W, or 9.2 amps (SPCR)
Don't forget that your CPU uses power from the 12v rail as well. (I welcome comments on how much.)
Overclocked video cards can use much more power than the standard reference cards, but most cards will probably artifact or crash long before they hit the slot+connector maximum wattages.
A PCI-E 1.x motherboard delivers a maximum of 75W to each PCI-E 1.x slot.
A PCI-E 2.0 motherboard delivers a maximum of 150W to each PCI-E 2.0 slot.
Each 6-pin PCI-E power connector delivers a maximum of 75W to the video card.
Each 8-pin PCI-E power connector delivers a maximum of 150W to the video card.
Watts = Volts x amps
Video cards are run on the 12v rail, so for our purposes, Amps = Watts / 12
Therefore:
The most a video card that requires no power connectors can pull under any circumstances is 150W, or 12.5 amps.
The most a video card that requires one 6-pin PCI-E power connector can pull under any circumstances is 225W, or 18.75 amps.
The most a video card that requires two 6-pin PCI-E power connectors can pull under any circumstances is 300W, or 25 amps.
The most a video card that requires one 6-pin PCI-E power connector and one 8-pin PCI-E power connector can pull under any circumstances is 375W, or 31.25 amps.
Most video cards actually pull far, far less than these maximum amounts. Note that video card makers must still assume that the user might want to run the card on a PCI-E 1.x motherboard, so they cannot assume that extra 75W from the PCI-E 2.0 slot will be there.
The above statements are fact, and not open to debate. When you ask how much a specific video card actually pulls, it gets much more debatable, because as far as I know, nVidia and ATi don't officially state how much wattage their reference card designs pull. You have to search around and find articles where reviewers have deduced how much power the video card consumes.
Below I list some video cards and the amount of wattage that reviewers say they use under full load. I list standard reference clock speeds only; overclocked cards will use more power (sometimes much more) and there are too many of those to list each one. Wattages listed are for the card only, not for the entire system.
Disclaimer: This list is only as trustworthy as the reviewers quoted. Sometimes the reviewers agree (see the 4850 entries), sometimes they disagree (note the GTX260 192 entries). I didn't make any of these measurements, nor would I know how to. Sources are listed in parenthesis. I may add more as I find them or have them pointed out to me.
nVidia GTX280: 178W, or 14.8 amps (XBitLabs)
nVidia GTX260 (192 stream processors): 122W, or 10.2 amps. (SPCR)
nVidia GTX260 (192 stream processors): 136W, or 11.3 amps (XBitLabs)
nVidia 9800GX2: 182W, or 15.2 amps (XBitLabs)
nVidia 9800GTX+ (two 6-pin PCI-E power connectors): 114W, or 9.5 amps (XBitLabs)
nVidia 9800GTX+ (one 6-pin PCI-E power connector): 80W, or 6.7 amps (XBitLabs)
nVidia 9800GTX: 108W, or 9 amps (XBitLabs)
nVidia 9800GT: 83W, or 6.9 amps (XBitLabs)
nVidia 8800GT: 78W, or 6.5 amps (XBitLabs)
nVidia 9600GT: 60W, or 5 amps (XBitLabs)
nVidia 8800GTS 512MB: 99W, or 8.25 amps (XBitLabs)
nVidia 8600GTS: 47W, or 3.9 amps
ATi 4870X2: 264W, or 22 amps (XBitLabs)
ATi 4870: 130W, or 10.8 amps (XBitLabs)
ATi 4850: 101W, or 8.4 amps (SPCR) (XBitLabs)
ATi 4830: 85W, or 7.1 amps (XBitLabs)
ATi 3870X2: 171W, or 14.25 amps (XBitLabs)
ATi 3870: 81W, or 6.75 amps (XBitLabs)
ATi 3850: 63W, or 5.25 amps (XBitLabs)
ATi 4670: 47W, or 3.9 amps (XBitLabs)
ATi 2900xt: 161W, or 13.4 amps (XBitLabs)
ATi 2600xt: 49W, or 4.1 amps (XBitLabs)
ATi x1950xtx: 110W, or 9.2 amps (SPCR)
Don't forget that your CPU uses power from the 12v rail as well. (I welcome comments on how much.)
Overclocked video cards can use much more power than the standard reference cards, but most cards will probably artifact or crash long before they hit the slot+connector maximum wattages.