I have a system that connects to the mains – and also a batteries designed for solar power systems.
Normal operation is for mains passthrough to connected items (PC, router, phone, TV, sat box, table lamps etc.), and, in the background, it tops the batteries up. When mains fail, the unit switches to battery supply automatically and my PC doesn’t notice. When mains restored, it goes back to mains passthrough and tops up battery again – and PC doesn’t notice.
You need a suitable battery as well as this type of unit. The bigger the battery (or, as I have, 4 batteries linked together), the longer you get power for. I have them in a shed with a mains supply and a cable to my front room for the supply but could stick them in a cupboard, I guess. I also top up battery water twice a year.
I can run PC, router, TV, phone, kettle etc. for 18 hours.
My system is old but this is similar – and – the reviews say they will clarify for you, and advise on battery(ies). Worth asking, or google for similar solar mains passthrough inverters.
2000W 12V low frequency pure sine wave off-grid power: Amazon.co.uk: Electronics
This maybe “over the top” but better than dell products which give limited supply to shut down only. This way, I just keep working. You could probably get away with 1 battery – unless you need to make coffee as well …………