If I'm ever doubtful that someone has unplugged something, I'll ask them to describe something that may or may not be on the plug.
- Color
- metal type
- "can you please read me the serial number stamped on the prongs of the power cable"
- "what color is the plastic inside the plug" Etc.etc.
Have not had it fail yet
Letter paper (8.5" x 11" | 215.9mm x 279.4mm) is kinda sorta pretty close to A4 (8.27" x 11.69" | 210mm x 297mm) so without having the two next to each other, it can seem like A4 is just a funny piece of letter, and vice versa. But to answer the actual question, USA and Canada (and apparently the phillipines???) use the "North American Standard" which is a terrifying mess in comparison to the beauty that is the ISO standard.
Edit: typos