Because I killed a PSU by plugging my PC into a gas generator once

By typing the question in the comment box, but that's not important right now

The "best" would be some kind of DC to DC converter, but I'm not sure there's anything plug and play atm because there's a wide range of specs laptops want. If your laptop happens to change with USB c PD or whatever the spec is that'd be the most efficient that I'm aware of. No sense in going dc->ac->dc if it can be helped.

There should be options avoiding AC depending on your scenario. Most laptops charge off of DC. Easiest way would be if all your things support USBC or similar.

Use an inverter-controlled one and you'll be fine. Our emergency communications shelter runs off one of those just fine, with a cheap offline UPS in there.

Yes, those that control frequency using the engine rpm aren't that great for most switching power supplies.

I'm guessing the cheaper ones don't have sine-wave inverters (they use a dressed up square wave which can be produced by purely digital electronics) so quality of the output waveform is bad. The power supply of the laptop (or PC) ends up having to work harder to cut out the extraneous bits of the waveform (that is it's job) but all that extra crap is just turned into heat. Laptop PSUs are small , so have less heat dissipation and likely aren't built for this. The ideal use case for these cheap inverters are purely resistive loads (like heaters) but even some less sophisticated electronics would probably be fine. Computer however, are generally designed for clean power.

If it's a sine-wave inverters and the generator is working properly then idk why it would matter.

Oh shit, you just made me realize when I get my first pay check I should really invest in a decent UPS. I had to sell my old one before moving state lines to condense space.