Whats on your turntable tonight?


For me its the first or very early LP's of:
Allman Brothers - "Allman Joys" "Idyllwild South"
Santana - "Santana" 200 g reissue
Emerson Lake and Palmer - "Emerson Lake and Palmer"
and,
Beethoven - "Piano Concerto No. 4 in G Major" Rudolph Serkin/Ozawa/BSO
slipknot1
“So here's something else for you to worry about: your local Power Company screwing up mains polarity.“

- Dick Olsher, Stereophile

Is this really a thing?
Ok so if I reverse the mains plug from the power conditioner what happens?  I might get a hum through my speakers if I plug it in backwards (reversed)? Or I get a hum if the power company has it reversed?  None of this matters with power tools and other appliances.  What is the effect of reversed polarity on a stereo?