I'm not sure there is a program to do that. There's isn't any information about wattage being sent from the psu to the motherboard, only power.
If you want to find out, you'll have to get yourself an amp meter, and only if you know what you are doing. If you don't want to go that route, you could try this PSU calculator, although reading the PSU101 will tell you it's not just as simple as counting the number of watts, but how big your 12v rail is.