The amps is for the whole system, not just the cards. They are looking for the 24amps on the combined +12v rails. Usually there is a sticker on the PSU that lists watts and amps to each rail. If you find the watts supplied to the +12v rail, divide that by 12 to get your amp rating. What PSUs are you looking at?
I would say get this one. I have this one and am very satisfied and impressed. Good price, great company, plenty of power to cover you for the next 5 years of upgrades, and plenty of rails and options and I bet you will never run out.