There is such a thing as a power factor correction capacitor, To get the right one requires someone analyze your system and the proper size depends on what is turned on.. Power factor is not an issue with water heaters and lights but it is with motors and may be with "electronics" .. However I doubt that fixing it will help you much.
Now.. if you are trying to use a generator that is a tad small to power A/C or Microwave (Which sounds like your issue) then there is a device you should look at.
This is a battery/inverter box, not unlike a UPS only way bigger, but it works a bit different too...
This one monitors power flow and when it sees a high demand (IE: A/C starting surge) it kicks in and "boosts" the power from the generator by adding some from it's inverter. Kind of like paralleling two Honda 2000i's but only when needed. Then once the A/C shuts off and the generator has "Excess capacity" again it drops back to batter re-charge mode to get ready for the next cycle.
I think Victor makes one, but it's been a few years since I looked at 'em so I can not even .. Some days I'm good. Some days GREAT, Today just good...
Google: Generator Boost System
Yahama 3000 watt generator with 500 watt boost systemI was not able to find the one I was looking for.. but this gives you the idea.
