What will happen to output of a transformer rated at 50 volts 60 hz when its powered by 115 volts 120 hertz versus 115v 60h?

Answer 1

A 50 volt 60 Hz transformer would work well at 100 volts 120 Hz, because the peak flux density in the core would be unchanged. Provided the insulation remained OK the VA rating of the transformer would be doubled.

Running it at 115 v 60 Hz would probably damage the transformer even on no-load because the core losses would be increased a lot with the flux density running at double the designed amount.