The plugs with the round earth pin and the conventional flat P and N pins are used extensively for the connenction between HID lamps and their ballast boxes. You probably won't see many of these in an industrial setting, but those shops that sell indoor gardening equipment have plenty of them. The lampshades typically come with a flex with a REP plug on one end, and the ballast boxes have the matching socket.
While this eliminates the confusion that arises when the lamp is plugged into a 230V socket without the ballast, it does little to stop the ill-informed trying to run 600W or 1000W lamps from 400W ballast units.
