Some new Honda & Yamaha generators actually produce high-frequency (several hundred Hz) and 3-phase AC output and convert it to something like 200VDC first, then they use an inverter to produce the 120VAC,
60Hz sinewave output. If the 200VDC is not well filtered, then you could see ripples (or sawtooth like waveform) at several thousand Hz riding on top of the sinewave.
They are more expensive (over $1000 for 3000 watt generator), but they can power computers, TV & other solid-state electronic loads far better than some cheap generators whose output waveform looks like a teenager's spiky hairdo (which will cause overheating of solid state devices & damage TV's, computers, etc.).
If someone wants to power TV, computer & other electronic appliances with engine generator, always verify that the output waveform is a regulated & clean sinewave (i.e., computer-grade sinewave). Noisy generator outputs can still power lights, refrigerators & heaters (in other words, motors & resistor loads are OK), but one should never power electronic loads (i.e., TV, computer, etc.)