It is false to assume that the state of the electrical supply is either on or off. This may come as a surprise, but not to me. In 2008, Eskom (South Africa's electricity suppliers) experienced similar faults. The mains supply voltage is 220v here. At one point, some devices started to fail in my house, and others, such as lights, continued to work, but significantly dimmer. We measured 180v at the plugs. There were similar outages in my area last year, where an outright cut-off was preceded by voltage drops. This outage is interesting because it is an example of a bug owing to false assumptions!
There have also been incidences where certain cables have been stolen [1] and that has caused the opposite: voltage spikes.
[1] I couldn't tell you which, or what kind, but I remember it has something to do with "the neutral"