That power bank serves a niche for me I've been searching a while for. I have a sound (white noise) machine I use for sleep, but it's pretty susceptible to brow

That power bank serves a niche for me I've been searching a while for. I have a sound (white noise) machine I use for sleep, but it's pretty susceptible to brown outs or dirty power and that's pretty jarring. It's powered by USB, and I've never been able to find a UPS that meets: - Small - Cheap (I wouldn't consider $99 cheap, but it's better) - Seamless switch between power and battery I've thrown a small battery pack on before but the battery wouldn't charge and serve at the same time.