My preferred inverter/charger manufacturer, Victron, has "UPS Mode" for their Multiplus units that will switch in 12ms. That's similar to many UPS's, though so

My preferred inverter/charger manufacturer, Victron, has "UPS Mode" for their Multiplus units that will switch in 12ms. That's similar to many UPS's, though some of the higher end ones are sub-10.