Does the amount of heat an AC-DC PSU generates depend on the amount of draw on the rails?

I have a 200 Watt mATX PSU but i'm using it in a really low power consumption enviroment. Ive got a sempron 2200 in the mATX board, onboard Video, 1 stick of ram, 1 HDD, slimline DVD and 1 PCI TV card. Is it okay to run with a smaller fan than it came with the PSU if im not going to be using more than 75 Watts, even by extravagant measurements?

Thanks for the info.