Here, in Broadband Hardware, please.
Phew! I’d posted it before you replied, glad it’s in the right spot
Some appliances contain a built-in surge protector, in the crude form of a varistor across the mains supply, after a fuse. If the mains voltage momentarily exceeds a threshold, the varistor absorbs absorbs the surge. If it's more than momentary, or the varistor shorts, the fuse blows.
I simply don't know if the modem power brick will have built-in varistor protection. I vaguely thought power bricks often do, but despite having spent an obsessive amount of time googling the topic, I can't find any evidence that I'm right.
In any case I'd really not dwell on it. I can argue a case that hypothetical scenarios might exist that would cause a varistor to fail on a regular basis every few months, owing to a badly behaved UPS. But since the fuse should then blow, that failure mode would cause the modem to become completely dead and bricked, rather than limping on weakly.
Thanks for looking into it, I appreciate it. I’m going to give the PSU a try anyway as it’ll be a useful bit of kit if I’m powering two modems when my other line is installed - it’ll make my install just that little bit neater!
Wow, that's quite a hefty bit of kit.....enough to power half a dozen modems if/when you get that many!!
If I was giving that a trial, whether direct from mains or via a UPS, I'd put a 2A fuse in the feed to the modem (as I do if powering from a 12V battery) just to feel a little safer.
And I think your wish to relocate the UPS to outside the kitchen cabinet is very sound.
I bought it a while ago to power some 12V fans I have cooling my VMware home lab cabinet and then discovered 5V USB fans before I got a chance to use it.
Re: fuses, would something like this be okay with a 2A fuse wired into the +ve line:
https://www.amazon.co.uk/dp/B01EFLXR36/ ?
As I say, I’m not super good with electronics so want to double check before I blow anything up
Thanks,
crgbt