These FAQs address my comments about getting what you pay for. Better
products have built in diagnostics and alarms to warn you when
components fail.
The most important feature if you have concerns about power quality from
your generator is to get an on-line or double conversion UPS. These
units convert all incoming AC into DC then convert it back from DC to AC
so you have complete isolation from the input to the output. Machines
that are sold as "Off-line", "Stand-by" should be avoided unless cost is
the most important factor, the protection is not much better than a
surge suppresser power bar with the bonus of battery back up.
"Line-interactive" machines are the middle ground providing a little
more protection by basically conditioning the line power by suppressing
the surges and boosting the sags and with varying degrees of filtering
depending the quality of the machine for other line garbage.
Line-interactive machines tend to get over worked when connected to a
noisy generator or a generator that the frequency or voltage wanders
allot, depending on the machine it may shut down, fail, or go to bypass
none of these condition is desirable.

Doug Hamilton

Zorro wrote:
These FAQ's are pretty good too.
http://www.powersentry.com/faq2.html
http://www.tripplite.com/support/faq/tech_surge.cfm
One thing I learned that left me feeling frustrated is that the protecting varistors wear out and most devices
will provide no protection when they are gone so you never know if the one you have is doing any good or not.