I doubt your analog clock needs 50 mA from 1.5 vdc, unless the circuit within the clock is defective. An AA sized alkaline battery is about 2000 mA-Hrs of capacity so a 50 mA draw would have the cell lasting about 40 hours. AAA sized battery would be about half that time.
As you say it is an analog clock I assume you mean there is an electronic timing solenoid like in most analog dial wrist watches. They have a 32.768 kHz quartz crystal oscillator that generates a one pulse per second output that drives the timing coil.
They draw very little current, in the order of 1 to 5 uA average. There is a small current current spike when the coil is triggered. Any 8 vdc DC power supply will likely draw orders of magnitude more power then the actual clock, but if you insist on having it AC powered you would be better off just making a direct AC to 1.5vdc power supply. Clock will stop when AC goes out. If you put a large, low leakage filter cap you will ride across short AC outages.