Dell OptiPlex N User's Guide (.pdf) - Page 19

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. Uninterruptible Power Supplies 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