No, you cannot just add the amperages. On the info card for the PSU it should list a maximum wattage for the two 12V rails combined. What is that for yours?
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Reply to EXT64
Wow, yes that is more than enough. I should have clicked on the link first (from your post I thought you meant it had only a 19A and a 18A rail, which would have been close). So from there, P=IV so Imax combined is 600W/12V or 50amps, plenty for a GTX260. Sorry for the confusion. I hope you enjoy your new card.
------------------------------Phenom II X4 940 BE 3.0GHz - 1.25V > GA-MA790GP-DS4H > XFX ATI 4850 1GB > 4GB OCZ Platinum 1066MHz 5-5-5-15-2T > PCP&C 610W
Athlon II X2 250 3.0GHz > GA-MA770T-UD3P > Sapphire ATI 4650 512MB DDR3 > 4GB OCZ Platinum 1600MHz@1066MHz > XP/Win7 Enter 64
Reply to EXT64
You should be fine with that power supply as long as it has the required pci-e power connectors.
750 watt is lots although I would go with a better manufacturer like CORSAIR, PC POWER AND COOLING or ENNERMAX EARTHWATTS.
But that's my 2 cents....still should do the job ok!.....
JQ
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Reply to johnnyq1233