I ran into an extremely perplexing problem a few years ago where shutting down one server connected to a UPS would kill the entire network until the server was

I ran into an extremely perplexing problem a few years ago where shutting down one server connected to a UPS would kill the entire network until the server was brought up again. The server was not providing any kind of networking at all, no DNS, DHCP, routing, etc. After wasting a lot of time remotely trying to diagnose this, it was obvious what was happening once I got on site. It turned out that once this server was shut down, the UPS didn't have enough power draw to power the other equipment attached to it, so a switch that was plugged into the same UPS would shut down as well. For some reason it had failed in such a way that it required a certain level of draw for it to function at all.