Thanks for the reply low_ryder.

I think you're right that I need a bigger UPS, as it can't handle anything more than a flicker (thought I had a larger one on the way, but 9 days later MicroCenter says it's unavailable, lol). This one can go in the nursery. There may be a power spike just before the timer cuts off, but ultimately the power allowance is still too close for comfort (and a larger UPS is needed).

Also, I think changing the 15 amp breaker out for a 30 is inevitable, but I hadn't realized that could be the cause of the flickers.