I read a blind comparison review years ago which included mains extension cable, in Stereophile I think. It did quite well.

When it came time to hook up the bedroom system, I thought I'd try it. I got some 12 gauge, 4 core copper stranded cable, which allows for bi- wire in a cable. I also bought WBT style banana plugs off Alibaba. No critical comparisons performed, but I'm pretty happy with the sound.

Cheers, Ian

1: Roon on Mac Studio, G-Drive 10TB, 818v3, 7200.2, UHD722, LG 77G4
2. 808.6, 8kSE
3. 218, 3200's
4: Rivian R1T - 18 speaker 1200W Elevation by Meridian premium sound system
5. G68ADV (croaked), G98DH (also croaked), [HD621, Syles SL-S/PDIF, MD600 (2*4TB), QNAP 469L (4*3TB), MS200], Ayre MX-R Twenties, TBD