Lak points out that something somewhere along the power path needs to be done to tame the AC nasties.
I find that the very top of the line Mapleshade power strip (which gives sonic benefits similar to many "conditioner" products) has subjectively enhanced the speed, clarity, and dynamic slam in two tube systems.
When I compared to directly plugging into the AC wall outlet, the effect of adding the power strip was as if I had shortened and cleaned up the power path.
So, you can't always assume the sonic outcome until your particular components are mated to a particular power strip.
When I read the review comments about differently designed power strips there is sometimes commenting about similar audible benefits, although I have not listened to many other brands.