GoSUV, if you can hear differences between USB cables, then I'd expect you to also hear differences between power cables.
On the other hand, you didn't notice a difference between your $20 block and direct to the wall. That suggests you won't notice the difference between power cables.
Confusing eh? This hobby is like that.
I think they can make a worthwhile difference, but the most important thing is that you can try before you buy. And, when you're trying them, if you can't tell the difference immediately, then just send them back and stop thinking about power cables. Just don't use that $20 block when doing comparisons. And if you have to agonize over seemingly minute differences, then stop trying and send them back.
PS. I've never tried any Nordost cable because the alleged Nordost house sound signature doesn't appeal to me. But from others comments, Nordost appear to have the widest range of love/hate/no difference responses of any cable company. There must be something that just clicks in certain circumstances, but I can't be bothered to find out what that is.