Ok, I stand corrected. The UPS units Ducati pointed to do have line filtering. The web site Ducati provided will get you to this
PDF white paper which describes what various UPS units do. Unfortunately, it is written for other engineers. The real point is in the tables summarising APCs product line at the end of the paper.
It does point out that the APC "Back-UPS" type of UPS is a switched system. A good system, but not as good as APC's "Smart-UPS" product line which does do a power conversion and new waveform generation.
Ducati996, thanks for the link.
The point I was trying to make, but failed, is that a lot of folks think that a UPS will take a dirty generator output and regenerate a clean waveform for running their sensitive equipment. Some will regenerate a clean waveform, some just filter what they are given, they all provide some protection. Just be aware of the differences.
If I were looking for protection from a bad generator I'd go for the waveform regeneration "Smart-UPS" product line. If I were just worried about line hits and cleaning up my power from light dimmers (etc.) the "Back-UPS" product line would do. If I were running speed controllers (electronic/SCR/thrysistor motor control) on multiple HP motors, or frequently starting multiple HP motors while on a standby-generator, I'd protect my sensitive equipment with the big guns double conversion or delta conversion products [multiple product lines here, look at the charts].
If I lived on a mountain/ridge top like Bob_Skurka, I'd do what he did and have a mains protection and also add a wall wart protection on my electronics. I'd also add a
secondary filter on my phone lines (in addition to the phone company protection), computer network, and antenna lines. I'd consider one of the higher end APC systems for my entertainment system and computers. But,
most importantly, check the protection units after each lightning storm. These surge protection devices do have a load capacity, but mother nature knows no limits. Sometimes, you have to replace the surge protector's guts. Sometimes you have to replace the UPS too, it may have given its all to protect your downstream equipment.