Hi Ben,I recognise the problems that brownouts or variable voltage/amperage can cause electrical equipment and fortunately my UPS unit has a special power "regulator" feature which is supposed to ensure a constant and reliable flow of power. If not enough power is being supplied by the mains system than the UPS will draw on its battery to bolster what is being supplied, whereas if there is a surge in the system the UPS will detect and 'filter' that surge before delivering power to the connected equipment (my computer and its monitor).
I feel much safer powering my computer through my UPS unit simply because I've lost a lot of electrical equipment in the past because for some reason my power supply has been unreliable (one year I had power surges on an almost weekly basis and I get several power cuts each year, usually because of bad weather).
Unfortunately my modem is never likely to be safe from power surges and brownout problems (not that I have had any of the latter) because there's no protection between the modem and the phone line and the modem is connected to the mains with only a surge protector and is not connected to the UPS.
Oh well. I suppose on the plus side I now have a much more modern modem which is considerably smaller and better-designed than my last one .
-Stephen.