I'm seeing easily a 5-8 degree drop on the stock AMD cooler too, and even my chipset temp seems better than before.
I think your problems lies with poor installation (either too thick a layer of thermal paste, or you have air pockets). Having the PSU so close wouldn't help either, so maybe this cooler should only be recommended for cases where the PSU is out of the way. I have the Arctic Cooling Silentium T2 case, and believe it or not, the PSU is well out of the way (as if by design)

Most of the other reviews on the net also show that it is significantly better than the stock AMD cooler.