Ground plug adapter is a great idea. I know what you mean about trusting house wiring. I’ve checked all my outlets after the house was built and at least 10 of them were wired reversed and a few had bad grounds.
So I finished the large print finally but I literally did not get closer than 2’ to the printer table while it ran (6 hours). The print looks flawless EXCEPT there is a “part line” at about 8mm up. It is not filament starving, it literally looks like the Z raised a few 10ths of a mm and continued to print that layer. This is similar to what I have observed quite a few times when I touch the filament or printer after supposedly discharging static. I print on a PEI surface on glass. I wonder if the printer itself is building up a charge too.