It's a specialized tool, but basically the plug get pulled out slightly (which isn't enough to disconnect power in the US), and then the tool goes over the line

It's a specialized tool, but basically the plug get pulled out slightly (which isn't enough to disconnect power in the US), and then the tool goes over the line and neutral pins, which supplies power from what is basically an UPS. After that, the entire plug can be pulled and capped (because you've got 120V across the exposed end of a plug now). Probably wouldn't work the same in Euro countries which have other plug types.