I have a home server that is on 24x7 protected by a UPS. The UPS monitoring daemon (nut) provides a hook for calling a script when its status changes, so I have it push a high priority notification to my phone via ntfy whenever it goes on battery or off battery. I also have it broadcast on mqtt so that in the future I can have a dedicated daemon that will collect stats and take other actions that aren't really approp…
How does ntfy compares to Pushover?
Pushover is an amazing tool and works well. In my obviously biased opinion though, I think that ntfy has a ton more features than Pushover and is fully open source. You can self host all aspects of it or you can use the hosted version on ntfy.sh for free, without signups, or pay for higher limits.
I suggest you try out ntfy;-)