Need wattage advice - 6870

I'm about to buy a 6870 off of ebay, but I have one potential issue that I would like to have settled.

My PSU is an Antec 550BP (550 Watts), it has 3 12V rails, one of which is dedicated to the GPU, another for the CPU and the GPU, and the last for molex/sata.

I've heard that the 6870 requires at least 500Watts (or suggests that much), but I was wondering if it would work with my PSU because of its multiple 12V rails.
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  1. it will work fine. the 6870 needs 2 six pin power connections. IF one rail has two that is great, if not use one from each of 12V2 and 12V3. general rule of thumb, for me, is the 12V1 is also the 12V for the CPU so i try to avoid using that IF i can.
  2. When looking at requirements for a card and you have the spec's of the psu and the psu has more than one rail you have to add the rails together for a total amps of the +12v rails. You do get a portion of the amps through the Pci-e slot as well as the 6 and 8 pin connectors.
  3. 550 Watts is MORE than enough. You did not specify your CPU (note mox nixs on HDDs/DVD drive)

    Typical i5-2500 system with a 6870 running furmark will draw around 350 Watts. You can find this in reviews.
    My i5-2500k OCed to 4.2, 16 gigs ram (DDR3-1600 CL7 @1.60V), single 6870, 2 SSDs, 1 HDD, and 1 Blu-ray writer. Measured at the wall 350 Watts, since a typical PSU is only around 80->85% eff that means the the Load on the PSU is only around 280 W.

    Reason Most GPUs over state PSU requirements is that there are a number of "Cheap"/junk PSUs out there that only delieve about 60-70 % of rate power once they warm up.

    Added if You have the BP550 plus you have two Pci-e pwr connectors
    1 x Main connector (20+4Pin)
    1 x 12V(P4)
    1 x 12V(8Pin)
    6 x peripheral
    6 x SATA
    1 x Floppy
    2 x PCI-E
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