[yladiz]

I'm not sure if you watched the video, but if I understood your first point, he debunked that by testing it on a wide range of plugs (sure it's anecdotal but I doubt he has such different plugs from other people in the US). Apparently the plugs that actually do have the bumps don't fit in a way that is safe (either they fit accidentally and/or fit too far forward, meaning the plug, with the holes engaged, is partially exposed). The reason plugs don't slip out is because of friction, not because of the holes.

My suspicion was the third one, and I suspect that was the original reason manufacturers did it. It's likely done now because of the machines that make plugs expecting those holes.

[rainbowzootsuit]

I have a number of locking cord ends (outlets) for extension cords that do use the holes to retain the male plug via ball detents. They require you to push a button to release the plug.

https://www.homedepot.com/p/15-Amp-Stay-Plugged-Cord-Replace...

I've never seen anything else similar.

I'm curious on the design of "hospital grade" plugs as that wasn't in his survey and I know that they are designed for higher retention force than commercial or residential applications.