There's actually a very inexpensive way to check and see if a different power supply will make a difference in a specific component (this only works, however, if you have a computer to do the testing on):
First run an RMAA loopback test. This establishes a baseline for comparison. For most soundcards, this involves a 1/8"-1/8" minijack cable. Google RMAA for the software needed to do the testing.
Next, run an RMAA with the amplifier in-line. Use a 1/8" to whatever input your amp takes, and then run a splitter such that the cable goes from the source to the amp, and back to the source again. This is the most complicated configuration, and can require two cables.
Finally, run an RMAA with the amplifier in-line, with the power supply swapped out. Compare results.
It's best if you can do the test 10 times and average the results to account for testing variation.
Chances are, if the power supply is appropriate for the amp in terms of specifications (it mostly is except for the cheapest of amps, excluding pro amps because from my experience they have good enough power supplies), you won't notice a difference.
If there is a difference, it will show up in testing. The idea is that you can use a layer of abstraction to compare the power supply differences: it's like putting an imaginary black box around the parts, and then only measuring the inputs and outputs to see if a difference exists. This methodology is a convenient way to do testing, and only costs a few bucks in cables. You can buy all of the cables at radioshack, and if your amp takes 1/4" you can find those at most instrument stores.