you seen my comment, buy a used commercial UPS for 800 and have better power quality than any "regen" unit cause thats what they are without the battery.
https://www.ebay.com/itm/APC-Smart-UPS-XL-3000VA-RM-5U-SUA3000XL-New-Batteries-1Yr-Wrnty-FreeShip/11...
https://www.ebay.com/itm/DELL-RACK-UPS-4U-2700W-208V-BATTERY-BACKUP-UNINTERRUPTIBLE-POWER-SUPPLY-H95...
https://www.ebay.com/itm/APC-Smart-UPS-XL-3000VA-RM-5U-SUA3000XL-New-Batteries-1Yr-Wrnty-FreeShip/11...
https://www.ebay.com/itm/DELL-RACK-UPS-4U-2700W-208V-BATTERY-BACKUP-UNINTERRUPTIBLE-POWER-SUPPLY-H95...