If the Korean standard is two prongs, that means that one is from the center-tap of the electrical provider's transformer. That prong will also be grounded.

It is irrelevant which of the prong feeds into which end of the diode bridge since they are merged at both outputs of the bridge.

I'm not against audio-system tweaks at all, and definitely believe that a good AC system helps, but I'd be extra-super skeptical of any company claiming that AC POLARITY can make any difference at all so long as the house wiring follows code.

Living room: 818v3, Audio Research D150, Maggie 1.6
A/V room: 861v8, DSP7200SE L/R/C, 4x DSP320 surrounds, ID41 + Roon, UHD722, Prime+PS