I was on the phone doing remote tech support with my 83-year-old mother today. At one point, I asked her to shut down her iMac (a model at least 10 years old by now) and then power it back up again. She selected “Shut Down…” from the Apple menu, and then … her phone line went dead.
I tried to call back—busy signal. She eventually called me back, and said that her printer and router had turned off briefly and were now starting back up. And the phone disconnected (though now it was back). Her iMac was still off, so she started that up again and everything seemed fine.
Her cordless phone runs off a base unit that is plugged into the landline and powered by the same surge strip that powers all the other devices mentioned. So it appears that her surge strip briefly turned off and on, disconnecting the phone call and restarting the other devices.
This coincided perfectly with the iMac shutdown. Now, it’s possible that she somehow jostled the surge strip and either toggled the power button or jiggled its connection to the wall outlet, but she denied this (and, as I recall, the power strip is pretty far out of reach/kicking range, on the floor behind her desk). So is it possible that shutting down the iMac caused the surge protector to power down and up again? Was it some reverse power surge as the iMac shut down? Or … ? The surge strip is at least as old as the iMac.