It is just one more degrading connection you should avoid, IMO. And other than a Home Depot type 12AWG extension cord ( which you could use it as a speaker cable, as it is said these days ;*), there is no such thing as a "high quality" extension cord. It's just either a wrong room setup with no aforethought to AC outlets and component location, or a room you are stuck with, as they say.
12AWG molded plug type (for $11.95 for 50') is the extent of high quality as far as extension cords go. Why not make a DIY longer power cord if you only need one AC component to power. I have made up to a 9'DIY power cord (from a very high quality power strip to my HSU sub) using high quality IEC and AC plug termination, with good quality 12AWG copper in between.
It comes down to what you are after. A garden variety extension cord is not a step in the right direction when compared to a long DIY power cord with quality parts. Up to you and what your aim is, and your thoughts on AC delivery. Some believe juice is juice, other come from the other camp.... Your ears and budget dictate here.
There’s no such thing as “degrading” with electricity. It’s all about providing adequate current flow and voltage for a given product. Just make sure any extension cable is the same gauge as the original power cable, or larger and you’ll be fine.
Okay, on further thought there is such a thing as “degradation” with electricity, but it has to do with “dirty” power, which is often caused by such things as industrial motors, compressors, etc. Obviously an extension cord cannot be a cause of power degradation.
It is so "non cumbersome" to get the materials, spend a few buck, and assemble a quality PC with appropriate materials to get where you want to be with quality AC delivery. UL is a good thing, no doubt, but with DIY, one is working with all ( or mostly, depending upon source ) UL listed components. Assembly of such is a matter of intellegence and the resulting performance. If you are one who is prone to poor workmanship, then buy a molded HD cord and enjoy your sound.
I appreciate quality workmanship and materials as well as the next guy, but a molded extension cord has nothing to do with sound quality. Especially when it's going to be plugged into a 50c outlet with spring-loaded connections.