I think an aftermarket power cable may slightly improve an amplifier's sound quality IF the amplifier has small power reserves, but not at all if it has strong power reserves. How does one test for power reserves? Turn off the amplifier while playing music; if the amp goes silent immediately, then power reserves are small, but if the music continues to play for several seconds, then power reserves are strong.
I used to own a Berning micro-ZOTL, and an aftermarket power cord made a noticeable difference in soundstaging depth. However, the same cord makes absolutely no difference on my Corda HA-2.
I have two tentative explanations. One, the difference was only in my brain. Two, amplifiers with very small power reserves are more sensitive to mains power quality, which some power cords claim to filter or improve.
Whatever you buy, never spend so much on cables that you could have bought a better headphone, amplifier, or source!