The 50W load (if that) isn’t the problem - a lot of cheap power supplies assume a perfect sinusoid which you get from a spinning mechanical source of electricity.
The inverter probably only does a few step approximation of a sin wave which is fine for most things, but clearly not for this power supply which browns out (I’m guessing during an extended period of 0v on the stair step sin approximation).
Whether your average power supply should be tolerant is unclear, but if it’s the only device playing up it’s clearly less tolerant of imperfect power than everything else.
The inverter probably only does a few step approximation of a sin wave which is fine for most things, but clearly not for this power supply which browns out (I’m guessing during an extended period of 0v on the stair step sin approximation).
Whether your average power supply should be tolerant is unclear, but if it’s the only device playing up it’s clearly less tolerant of imperfect power than everything else.