This Leviton model 16693 three prong plug is idea for older two wire equipment when you want to add that extra bit of safety. The plug provides Ground Fault monitoring to older equipment that was not designed with grounding in mind. In the arcade and jukebox industry grounding did not become common until the 1970s, so this simple plug may save you a lot of wiring time, plus in some jurisdictions Electrical Codes do not allow for adding ground wires to equiment that was not previously grounded.
Why you need GFCI plugs or outlets
PDF of the instructions are in English, French, and Spanish.