VAC products have a lot of experimentation and voicing behind them, and the stock cords with the amps were chosen for a reason. Aftermarket cords have utility with cheap products sold with improperly shielded power cords, but they can really mess with high frequency reproduction on elite products and have to be chosen with great care.
The current capacity of a power cord that is only six feet long and connected to a tube amp that draws at most 10 amps on peaks is a non-issue (the stock cords are 14-gauge, which is more than fine for the length and the product -- if you have to run 75 ft. to a big Krell, that's another matter, but no need here). Kevin claims to have tried some thirty power cords with my VAC Renaissance 140/140's monoblocks before choosing the stock cords -- if you want the amps to sound like they were designed to sound, stick with the stock cords.