It's highly unlikely that the manufacturers COULD do anything to power cords or power conditioners that would reliably change the sound. It is possible for cables, although the only tools available to them would make the cables less accurate (in a technical sense) than 12 AWG zipcord. It's possible that someone with overly bright speakers might like a cable that rolled off the highs (though that strikes me as an odd way of going about things--why not just buy more accurate speakers in the first place?).
Frankly, I think the manufacturers rely more on expectation effects than real engineering.
Frankly, I think the manufacturers rely more on expectation effects than real engineering.