My first thought would be a tuned LC filter, resonant around 120 Hz. That would have avoided the noise problem and been far more reliable, and a whole lot cheaper.
When I was designing test equipment for factory floor operation we almost always put a Sola Brabd constant voltage transformer ahead of the controls and instrumantation power input. It was always cheaper than even one service call to fix a machine, and it gave us a reputaion for producing very reliable testing machines. The noise on the waveform on the scope traces looks a bit like it comes froman inverter drive circuit for a medium horsepower motor.
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