If the voltage ranges are unstable (ie: power stays on, but the actual voltage amount varies a great deal with the 220V regular), then I think that's the kind of situation exactly where an AVR is useful. This reply has many of the most useful measurements of this problem on https://aikidohistory93692.yomoblog.com/40402359/a-secret-weapon-for-uninterruptible-power-supply-symbol