How do I condition power between a generator and a UPS?

Solution 1:

Use a SmartUPS. The UPS use the power from the line to charge the battery while the output from the UPS is from the battery. APC call that way True Online. The line stay more isolated than like a backups where it's a on/off to go on battery in case of a powerloss.

Edited: The input range must be between 50 & 60hz, else it will fall on battery

Solution 2:

Rather than adding a conditioner, get a generator that is meant for office/home loads. I'm guessing the generator you have now is meant for building sites & power tools with a specific type of electrical motor in them.

A domestic type generator will also be more quiet and efficient. And you can move it & use it for your fridge/freezer when needed.