Re: colour me sceptical
A long time ago, when round pin sockets were still lingering in older UK houses I had a unversal plug. There was a slider adjacent to the flex entry point which would uncover different sets of holes in the plug face to let different sets of pins fall through - I think the selected pins could be rotated to lock them into place.
It was very clever except for one detail. It didn't have a conventional cable clamp, maybe it would have got in the way of the slider. It had plastic fitting which just clamped round the cable with a self tapper so that pulling the cable would have jammed the fitting up against the side of the plug and held it firm that way. The self tapper was so positioned that it could easily bridge the line and neutral....