[GreenKeys] Anyone know what this is (beyond the obvious)?

[Jim Haynes]

I don't see it in the parts books for the KSR or ASR sets.  LESU type
mountings were used in a few other products, such as reperforator and
transmitter cabinets for torn-tape message relay systems.

My guess is that it might be a 48V supply for operating relays and
stepping switches.  There was another 48V supply I'm more familiar
with that does not use a Sola transformer.

When you get your hands on it you can see if there is a part number for
the whole assembly, and perhaps the transformer will have its output
voltage printed on it.

At least you got it cheap.