I never expected power cords made a difference. Then I got a used 2M Audio Art Power I Classic cable, used with a big class D amp. Immediately heard subtle but worthwhile differences. Got a 2nd one of these (1.5M) and put it on a tubed headphone amp. Heard a slight but worthwhile difference.
These are budget cables, bottom of the line in Audio Arts lineup, but they made a positive difference for me.