Powercords do matter, but they can only degrade sound. Once you get an adequate power cord, the sound will not be degraded.
Many expensive power cords have all kinds of fancy claims and when you ask them what gauge they are they say "14, anything more than that is a waste" which tells me they don't understand the issue.
But don't think you can tune the sound with a power cord. If you are trying to tune your sound with power, you are degrading sound with inadequate cord.
Jerry