Need Help with PSU for 7800gs!

So after 4 years with my trusty 9700pro I finally have found a card deemed worthy of an upgrade for my aging agp system(which i am very happy with by the way). I have absolutely no interest in pci-e and any of that other "hoopla" at the moment but that may change next year...Anyway back to the purpose of me making this thread. I am currently on a 3 year old 350watt power supply and immediately realized this would not be sufficient for the 7800gs (The overclocked BFG one in case you were wondering) so the first thing I did was go on tigerdirect and get a better power supply and I ended up getting this one http://www.aselabs.com/articles.php?id=85 (ThermalTake Silent PurePower 480W PSU ). I was soo excited about upgrading that i rushed to just grab the first psu that i thought was good, but I later found out that its not really about how many watts your psu has but more about how many a's your 12v rail has... Unfortunately I didnt realize this sooner because I had already placed the order without researching this issue/requirement first..Now my problem is that on the BFG site,they recommend A "minimum 400W system power supply (with 12V current rating of 20A or more)" My problem is that I have now found out that my PurePower 480W psu only has a 12v Rating of 18A and thus i am now worried that I just purchased a new psu like a fool and it will probably be useless in powering my 7800gs. Any advice? Can the 7800gs manage on a 18A 12v rail? Also can i get a refund from tigerdirect or at least an exchange or something if It doesnt work with my card? ( I bought both the psu and card from tigerdirect,simultaniously)Any advice,help or tip would be greatly appreciated, As i have always been an ATI guy and im not really too familiar with nvidia.

 

Find a different place to buy from and it should be fine just make sure the 12v rail does not go blow 12 v at all or even close to it and it should be fine because I am buying one and I only have a 17a 12v rail on a 450 w psu.so just when u get it check volts before doing anything