Can a power station work as a UPS?
Most portable power stations can act as a basic UPS: 25 of the 27 current models we track publish a switchover time, from 10 to 20 ms. 9 switch in 10 ms or less; the cheapest of them is the EcoFlow RIVER 3 Plus ($299 list). These are the makers' figures; a desktop PC may still restart on a slow switch, so test yours before relying on it.
Switchover time, fastest first
Switchover = how long the outlets go dark when the grid drops, as each maker states it ("under 20 ms" is shown as 20). Some makers limit it: only certain outlets, only with a mode turned on, or not while the station is charging; the source note on each model page says which. Runtime: desktop PC + monitor (90 W) and a Wi-Fi router (15 W), from usable capacity as everywhere on the site. No published switchover time: Jackery Explorer 300, Goal Zero Yeti 1500X.