I have a pretty revealing system which allows me relatively easy to hear the difference sometimes when changing any of the component. My system consists of Bryston BIT20, 28B SST, BP25, BDA3, OPPO 203, Cambridge CD transport, Marantz SR6012 receiver for movie playing, Kimber 8TC, Bryston and Tributaries XLR ICs, and all Pangea PCs. I'm currently in the process of trying out and determining the right power cable for BIT20.
For quite a long time I thought that it would not make any difference to change the PC for BIT20 since it's an Isolation transformer. So for quite a long time I just used the stock PC for it but only changed the wall outlet to a PS Audio outlet. And I was quite happy with the sound of my system. At one point late last year out of curiosity I used Shunyata Venom HC on my receiver with a Pangea 15A to 20A IEC adapter to replace the BIT 20 stock PC. I immediately noticed a tighter and deeper bass with the new cable. But I didn't like the mid and high frequency range sound so I went back to the stock PC.
At the end of last year when Morrow cable was on sale I bought their MAP4 Grand Reference power cable to try out on BIT20. Now the cable has been broken in for more than 50 days and it totally changed the sound of my system. The sound becomes more clean and clear with extended highs and sweet mid range with tighter bass and wider sound stage. I'm enjoying my system sound more than before. Now I'm still debating if I want to keep this cable and done for it or upgrade to Morrow's Elite Grand Reference PC, or return the cable (still within the 60-day free trial period) and use the Cable Company to try more cables.
So from my experience and in my system changing the power cable for BIT20 did make a noticeable difference.