There are, far as I know, 3 types of generators for this discussion......
Small "Contractor" jobs, portables usually in the less than 4,000 watt range (NOTE not firm on that) and with motors that run at 3600 RPM are "Mostly sine wave" but can produce a very dirty wave with some very nasty spikes... Alas, I can not link you to the article on thiese as it is a "Members only" area... (I happen to be a member, tough I tell folks that I do not plan on renewing.. You see. when the Life membership expires... So do I).
The next type is larger traditional generators, Generally 5,000 watts and up, Genrally these units have low speed motors 1800, 1200, less than 3,000 in any case.. These tend to produce fairly clean power. A good example of this type is the Onan Emerald I sit on from time to time.
I have never scoped it, mostly cause the scope I had was not really good enough for the job. but they are fairly clean.
The third type is the Inverter generator, nearly all (In fact all that I have ever heard of) are True Sine Wave, clean and pure.
I tried to find the article, Odds are your local library has it but I could not find the article with the searches I used.
But they covered the issues with a lot of the contractor models.
I have no problem with any of the electronics in the house on the Onan.. I tend to use caution with smaller generators though less they are Inverter type.
There is no way a non-inverter generator can produce a modified sine wave/modified square wave..
Distorted sine yes, modified no.
Home is where I park it!