Curiosity got me last night, and I googled a bit for references to commercial 25Hz power, and I found this tidbit buried in a railfan newsletter pertaining to the Pennyslvania Railroad and Penn Station in Manhattan:
"Up until the late 1970's, at least, Consolidated Edison still supplied power billable at their meter, depending on your location in NYC, at DC, 25 Hertz and 60 Hertz, in a variety of voltages. ...
At the turn of the {last} century {and} well until the 1940's both DC and 25 Hertz were fairly widely used as power for commercial establishments; after all, Edison started the city off with a DC system. ...
The PRR had a 25 Hertz power supply feed account established with Consolidated Edison in the 1930's when they strung catenary into NYC. The interesting thing is that this was supplied and billed by Edison to the PRR at catenary voltage (11 kV at 25 Hertz), and not at 132 kV as done by the PRR's other 25 Hertz suppliers ...
The Consolidated Edison 25 Hertz supply generally was the highest cost power to the railroad, even well into the Amtrak era, ..."
I knew that DC was commercially available in places in Manhattan in most of the 20th century, but it's news to me that commercial 25Hz was available in the area.