My two monoblock amps, have 12’’ power cords. The shorter the better, different lengths do not matter. In my opinion power cords and speakers cables should always be kept as short as possible, that’s one of the many reasons for monoblock amps. Time alignment with power cords is silly. 😁
Dealer stated "2m works the best for it to really filter".
It’s the opposite, the shorter the cable the less chance of it picking up noise.
Mike