Basically as the title says. We have semi frequent power outages where I live. The noise machine in my daughter’s room goes out and wakes her up. If I were to buy a USB powered one, plug it into a power bank like one of those 10000ma ones you get for charging cell phones, would it have continuous power. Basically like a cheap UPS
Per the post prompt, a fussy sleeping child would not do well with the ‘OH SHIT SAVE YOUR WORK NOW, WE LOST POWER, EMERGENCY’ buzzer going off every 10 seconds.