Obsolete 125 V, 15 A / 250 V, 10 A duplex outlet
A patent for this obsolete plug and socket was filed in 1915 under US Patent 1,179,728.[26] It predated the NEMA sockets and plugs, but is similar to NEMA 10-20. The plugs and sockets used in countries such as Argentina, Australia and China are based on this type.
Man, you have good eyes, I didn't notice that until you pointed it out. I did notice the rubber housing was kind of large for the 2 prongs but didn't look any closer .
here's a pic with the blade cleaned up