My housemate's desktop has a noisy power supply

[user181]

Originally Posted by dieseljeep

There's been a trend for many years to provide an isolated ground for computers and similar equipment. It's not dependent on the raceway or the BX cable armor. It requires a separate ground conductor going back to the service panel ground bus. The bright orange receptacles you see in some locations are isolated ground receptacles.

That's mostly in commercial facilities, data centers, and hospitals. There are a few reasons for doing this, but my point was that regardless of grounding, SMPS are very noisy, electrically. Noise gets conducted back through the power mains, and it also gets radiated.