Art Todesco wrote:

I have a computer and DSL modem tied to an old UPS (with new
batteries). When I have a power failure, the computer keeps right
on ticking, but I always have to restart the DSL modem. I've even
restarted the modem while running on the UPS and after its restart,
all was fine. I am assuming here that the switch over time is
killing the modem. I looked at the modem and its walwart. It says
12 VDC. I was wondering if putting a few thousand micro farad cap
across the 12 volt line might help. Anyone have any experience with
something like this?

I would agree that you probably could use a newer / better UPS with a
faster or no switching time. It is also possible that the DSL modem's
cheap power supply has inadequate filter caps, or they are cheap and
have failed. A new power supply may solve the problem, or adding a big
cap as you indicated should also allow it to ride through a few cycles
of outage while the UPS switches.