Line Conditioners; Ups - Dell OptiPlex NX User Manual

Surge protectors, however, do not offer protection against
brownouts, which occur when the voltage drops more
than 20 percent below the normal AC line voltage level.

Line Conditioners

Line conditioners keep a computer's AC power source
voltage at a fairly constant level and, therefore, can
handle brownouts. Because they provide more protection
than surge protectors, line conditioners cost more up to
several hundred dollars. However, these devices cannot
protect against a complete loss of power.

UPS

An uninterruptible power supply (UPS) offers the most
complete protection against variations in power because
it uses battery power to keep the system running when
AC power is lost. The battery is charged by the AC
power while it is available, so when AC power is lost, the
battery can provide power to the system for a limited
amount of time from 15 minutes to an hour or so
depending on the UPS system.
UPS systems range in price from a few hundred dollars to
several thousand dollars, with the more expensive units
allowing you to run larger systems for a longer period of
time when AC power is lost. UPS systems that provide
only 5 minutes of battery power let you conduct an
orderly shutdown of the system, but are not intended to
provide continued operation. Surge protectors should be
used with all UPS systems, and the UPS system should
be Underwriters Laboratories (UL) safety-approved.
Maintaining the System 2-5