Need to find a power supply for graphics card - can you combine the total amperage of dual 12v rails?

Question

I'm looking for a new power supply for my HP computer to power a hungry graphics card such as the Nvidia 7950GX2. On Nvidia's page, they recommend:

"The minimum recommended power supply for a single GeForce 7950 GX2 is 400W (with 12V current rating of 27A)."

The 500w power supply that I am looking at has dual 12v rails - one 12v rail has 17amps, the other has 19amps. Here are the specs:
"+3.3V@32A, +5V@35A, +12V1@17A, +12V2@19A, -12V@0.3A, +5VSB@2A" from http://www.newegg.com/Product/Product.asp?Item=N82E16817103937#spec

When a graphics card requires 27amps from the 12v rail, does the amperage all need to be on ONE rail? Or is it ok to combine the total amperage of multiple rails (19amp + 17amp = 36 amp 12v rail)?

Thank you in advance for any help :)

I'm looking for a new power supply for my HP computer to power a hungry graphics card such as the Nvidia 7950GX2. On Nvidia's page, they recommend:

"The minimum recommended power supply for a single GeForce 7950 GX2 is 400W (with 12V current rating of 27A)."

The 500w power supply that I am looking at has dual 12v rails - one 12v rail has 17amps, the other has 19amps. Here are the specs:
"+3.3V@32A, +5V@35A, +12V1@17A, +12V2@19A, -12V@0.3A, +5VSB@2A" from http://www.newegg.com/product/product.as...

When a graphics card requires 27amps from the 12v rail, does the amperage all need to be on ONE rail? Or is it ok to combine the total amperage of multiple rails (19amp + 17amp = 36 amp 12v rail)?

I have a PCI-E slot and I know that particular power supply fits my computer. I dont plan on SLI in the future. I'm just wondering if that particular power supply, with a 19amp and 17 amp rail, is good enough to power that particular graphics card that requires 27 amps.

I am a bit more confused at the moment because Mysticman says that it will be fine, whereas Linuxiac seems to be saying that it all needs to be on one plug (and wont be fine?)

Answer 1

Keep in mind when nVidia is saying that they are accounting for the entire system, not just the video card, because most power supplies only have 1 12V rail. The card itself only needs about 14A, so the power supply you are looking at will be just fine, the video card will run on one of the rails, and the rest of the system on the other.

Answer 2

Ouch! - 268W combined for the 12V and 5V, that's not much. Sounds like an honest "300W", but not enough to handle a 460 - the guide figure is a 450W, and that means 450 good quality watts, not a bargain basement noname model that claims it but can't deliver.

Answer 3

The connector that powers the GPU card has to have the full rec. power available on that plug harness. There is no way to combine the output of two regulators at that point, and will actually cause 'ground loops' that would destroy them, and the entire PSU.

So, find a recommended PSU and use it, or get a card that can use your PSU!

Answer 4

Youd better check to see what your mobo will accept!

Answer 5

Get a better one. If its SLI-Ready, you're good to go.