Re: 'Safely Switched'
I'll give you a hint.
If you have a cordless phone, this was always the case.
The way BT solved it for wired phones isn't a generator at the exchange. There's basically a UPS in the street cabinet now. And that could give out after a few hours, too. The street cabs are running hundreds of watts of adaptors and the only connection back to the exchange is fibre, not power.
So the solution to this is very simple. You do what BT used to do and now still do. You put a UPS on the router/adaptor/whatever else needs powering.
£50, a UPS (one of those in the form of a very thick extension lead), problem solved. Especially in a rural area getting lots of power cuts. Hell, you can even plug an LED light bulb into it so your elderly relative isn't fumbling around in the dark for candles, and it'll keep the wifi up so they can stay browsing on their phones and give people a call via Facetime or Whatsapp (what's that? You think elderly people who grew up being adults in the main home computing era are functionally technically useless as their own grandparents were? Nope... I live in a council retirement estate, basically, and all my neighbours have wifi, mobile phones, Netflix, etc.)
And I'll tell you how I know this works:
I live in a rural area that gets lots of power cuts. 6h40m of outage only the other day.
I brought an antique (20+ years old) UPS with me. I even went to the expense of a new battery (£30) for it.
It can run the router for approximately 20 hours or more.
I also have a backup solar system with 4KWh of batteries. They can power the UPS for literally days if required to, and perpetually through the summer.
And what happens when you power the router off a UPS and you have a blackout? Your Internet stays on. Your Digital Voice (actually just SIP) phone stays on. Because the cabs are still powered, but only for DSL... they no longer want to power every telephony appliance in the entire town in a blackout.
Many's the time that I have carried on gaming online during a complete powercut through the entire town.
Many's the time I didn't even realise the power was out BECAUSE I was gaming or watching a movie in the dark and only realises when I went to switch the light on.
In the blackouts, I still have full access to the Internet via both DSL and 5G (but surprisingly, DSL just doesn't drop out in any power cut I've had, probably because of the Digital Voice requirements nowadays).
Buy yourself and any elderly relative a £50 UPS. Plug the router, a phone charger and a lamp into it. Carry on with your life.
And especially if they are vulnerable enough to use telecare... Redcare etc. are now IP-based services. The replacement is LITERALLY a UPS because the solution was LITERALLY a UPS beforehand anyway (there's a reason telephony and PoE both use 48V and why that's a nice multiple of the 12V you can achieve with standard lead-acid batteries). And if a £50 UPS saves their life... it's worth it. Compared to paying for telecare services to put an EXTRA UPS in every street cabinet in the country just for that for a handful of customers.
The argument of "we must still have traditional powered landlines for all" has come, been lost, and gone decades ago. Buy a UPS. It'll last as long as the mobile base station's UPS, or the DSLAM at the local cabinet's UPS. And that's plenty of time for them to tell someone "My power's gone out, can you come over because I don't know what I'll do if this medical equipment turns off". Which is literally all you need. And electricity providers will literally turn up with individual generators in those instances, it's why you register vulnerable people with your utility providers.