The AC voltage at the wall doesn't matter, your computer's power supply converts that into lower voltage DC.  As far as I know, a 12V rail supplies a lot of the power to a video card.  So a good graphics card would probably pull over 25Amps at 12V DC.  At the end of the day, that isn't something you need to worry about since computer equipment manufacturers report the maximum Wattage requirements to you.  Those computer parts can then be paired with a power supply which is also simplified to watts in the "big label" literature.  If you're building a computer it is good to know the amperage at each voltage, but it isn't a necessary consideration for this discussion.