I wonder if the diplomatic staff get some kind of orientation advice - perhaps along the lines of the 1943 film for GIs.
Maybe this one?
The US Embassy here in Norway moved a few years ago, and I had the opportunity to take a tour of the old building some time back. Note that the building was from 1959, so it might very well have changed since then.
In the “public” areas such as the meeting rooms, library, ballroom and normal offices where anyone could potentially get invited the outlets were standard 240V as you would find in any other building in Norway. However, one section of the building was more secure with “No phones allowed”-signs, thick and heavy (probably metal-lined) doors and so on. The outlets inside that area were all US-style plugs, I assume 120V/50Hz.