One will always get advice to not run an interconnect (or speaker wire for that matter) too close to power cords. This advise suggest that power cords could be one source of noise in a system by way of EMI )electric magnetic interference) contamination. So the question is why haven't this source of noise have been addressed in consumer products.

I think it was Skeptic suggesting that shielding after market power cord [that is not shielded] might violate UL safety codes for power cords. So given that UL approve a shielded power cord design, wouldn't this power cord outperform unshielded power cords in term of less environmental contamination, most notably the 60 Hz hums?

I believe the answer to above question would a definite yes. Just take a look at a typical HT setup with all type of wires going everywhere and twisting around each other (like my setup), and one will note that shielding power cord might not only sound like a good idea, but a necessity to reduce system noise