When conversation turns to a debate of VoIP vs POTS one of the common arguments in favor of keeping at least one POTS line is the idea that a plain vanilla phone doesn’t require AC power. It’s power comes down that very same POTS line from the phone company, so in theory it remains operational in the case of a power outage. This is fast on the way to becoming a myth.
The idea itself is not wrong. You could have a very plain phone on your POTS line, and it would work during a power outage. However, the simple fact is that at least in the US…almost noone has a simple line powered phone anymore.