I just found this post when trying to research the same issue I’ve been having. I’ve ran my basement fridge off the AC70 (regular version, not P) for about 7 months with no issues. Today, my fridge was repaired (a freeon leak so it needed a new set of coils and evaporator) but also a commercial relay was installed to replace the fridge’s existing dinky one. I’m guessing that since it has the commercial (and much larger relay) installed, that has something to do with how the compressor draws power. Before the repair, the fridge was the only thing running off the AC70, drawing about 150 wats when compressor and internal fans were running. Post repair, the fridge draws around 375 wats and the compressor shakes constantly where I see no such behaviour from the standard wall plug. I’ll test again with a 5 minute break between unplugging and re-enabling AC power to see if that makes a difference, but I doubt it :( the commercial relay appears to be the issue. For reference, the fridge in question is a standard residential whirlpool with only a fridge, not a freezer, and an older (mid 2000s compressor)
If the voltage fluctuates which throws off the magnetic rotation of the AC motor, it will jerk/shake/rattle. Likely caused by the inrush current resulting in this behavior.