If your voltage ranges are unstable (ie: power stays on, but the particular voltage stage varies a lot from the 220V regular), then I think that's the kind of situation in which an AVR is helpful. Although that's a whole lot better than the output we've been lead to assume https://byd70245.bcbloggers.com/32988605/the-definitive-guide-to-uninterruptible-power-supply-review