Air carrier Captain reported that smoke was detected with subsequent failure of the APU during push back. Flight returned to gate and aircraft was refused.

Narrative

On Day 0; I was operating Flight ABCD ZZZ-ZZZ1. Upon pushback; got smoke detected. I have then asked ground crew to stop the push and check for outside smoke; and flight attendants on the inside. Smoke was not detected anywhere and shortly after we lost all power. And then got about 10 master cautions. Maintenance then came onboard and deferred the APU. Considering all the above and having a probationary FO (First Officer); I decided to refuse the aircraft. Operations provided another aircraft and uneventful flight to ZZZ1 was accomplished