[tlb]

One scenario: there's a short circuit somewhere, say rats chewing through insulation. This can cause a very high current through the short. A non-inverter 4500 watt 120 volt generator might have 0.2 ohms coil resistance, so the short circuit current can hit 170 volts / 0.2 ohm = 850 amps. When the shorted branch's circuit breaker trips, the inductance in the generating windings wants to keep that 850 amps flowing for at least a few microseconds, and it gets distributed across everything else that's still connected. Depending on what else is connected (hopefully including some surge protectors) the peak voltage can get into many kilovolts.

The circuit is something like this:

  voltage source -- parasitic inductor --+- circuit breaker -- short
                                         |
                                         +- circuit breaker -- your PC

[pseudohadamard]

More generally, for the previous poster, look at what happens when a magnetic field collapses suddenly, you can get kilovolt spikes. There's probably a ton of YouTube videos demonstrating this in various ways, it sounds like the sort of thing that Electroboom would do. Normally this is handled via snubber circuits which dissipate the energy before it can do anything, but in exceptional cases it could end up going where it shouldn't.