18amp too low?

[Ruger22C]

Video card 7950GT by BFG, says it should have 22amp. But the 500W PSU is only 18amp. How much performance will I lose? I plan to get a new PSU later. But for now that's all I could afford with an 8pin CPU connector.

BTW here's what I bought:

1 MSI P6N SLI Platinum LGA 775 NVIDIA nForce 650i SLI ATX Intel Motherboard - Retail
Item #: N82E16813130081
Return Policy: Limited 30-Day Return Policy $144.99
1 Seagate Barracuda 7200.10 ST3250820AS 250GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
Item #: N82E16822148142
Return Policy: Limited 30-Day Return Policy $66.99
1 Intel Core 2 Duo E4300 Allendale 1.8GHz LGA 775 Processor Model BX80557E4300 - Retail
Item #: N82E16819115013
Return Policy: Processors (CPUs) Return Policy $117.00
1 Rosewill RP500-2 ATX 2.01 500W Power Supply - Retail
Item #: N82E16817182016
Return Policy: Standard Return Policy $49.99
1 G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400PHU2-2GBHZ - Retail
Item #: N82E16820231065
Return Policy: Standard Return Policy $104.99
1 Rosewill R103A Black SGCC Steel ATX Mid Tower Computer Case 350W Power Supply - Retail
Item #: N82E16811147010
Return Policy: Standard Return Policy $25.99

 

[blackangst1]

Is there only one 12v rail? If its a newer supply should be two rails. In which case add the two voltage ratings together.

If, however, you only have one rail at 18a, you cant run that card.

 

[Ruger22C]

Oh, no . 2 rails. Didn't know.

 

[Ruger22C]

Thank you.