Other than the tubes vs. solid-state argument and the class A vs. class B argument, an amp with a larger power supply will often sound louder and more dynamic due to its ability to drive more current, i.e. dynamic headroom. When I was in school I learned this and was amazed at a demo at my local Circuit City. The salesman there was comparing a 26 wpc Harmon Kardon receiver versus a 90 watt Pioneer integrated amp. I and others there expected the more powerful Pioneed to blow away the HK, right? So we were all amazed to hear not only that the HK had much better sonics, it played much louder. The sales guy then asked someone to stand on a scale he brought in and the HK was twice as heavy, hence a much bigger power supply.
