Every amp I've owned in the last 20 or so years I've made my own custom cord.
Because every house has it's own sound (electrically) I find that each house and component has their own relationship to each other. When I change out an amp it takes about a week or so and I'm designing a cord specifically for that unit. I also find (for people tuning their AC) that resetting their wall outlets per amp is a big deal along with the circuit panel.
If I may I'd like to give a free tweak out to folks. When you change out your cord you obviously have your amp turned off. While turned off loosen the shipping harness of your transformer, raise the transformer up slightly and set it back down. Your amp will sound more open and powerful. I recommend getting rid of the shipping harness altogether, but even re-setting the mechanics of the amp can be a pretty big deal.
mg