Should I upgrade power cord for my preamp?

I was a skeptic until I tried a PS Audio Premiere Power Plant. It made a huge improvement, so I decided to replace all my power cords with PS Audio cables. I used AC-10s for my amps and the PPP, AC-5s for everything else. It made more improvement than any interconnects, and I had dedicated 20 amp lines to start. They did take a while to break in, but both my wife and I heard a sudden step-up one evening. I wrote the company and asked if they ever got mail like that, and we were not the first to experience it. The Cable Company will let you borrow cords, and I expect you will hear clear differences, too.