Not only are there brownouts and missing phases in AC current, which any UPS capable of handling the load will intercept, but voltage peaks are a permanent threat to system operation - and to your components. Hence, it is very important to use multi-outlet power strips that include surge protection. Almost all UPS devices include surge protection circuits for devices running on a battery charge. Others, such as Belkin's product, offer two additional power outlets, which aren't battery buffered, yet surge protected. They can also accommodate secondary devices, which you may not require in case of a power outage (printers, certain network devices).
Power Fluctuation Leveling
The surge protection feature actually goes much farther, as a decent UPS does more than to just offer protection from power spikes. It also takes care of leveling all deficiencies of the power grid, providing a steady and stable 50/60 Hz AC to the client devices.
Network Transient And Phone Line Protection
All interconnects that create physical connections between PCs using many different networks are a potential source for surges. So-called transient voltage suppression diodes are used by modern UPS devices to surge protect network interfaces and phone jacks. Almost all UPS devices offer a RJ45 network port with transient protection. Others also include a RJ11 connector, but since phone lines are rather uncommon these days, you won't find too many UPS units with phone line protection in the low-end and mainstream categories.
Management Software And Interface
As you will see later, the UPS devices come with comprehensive management software. The software does not only allow users to monitor the UPS status, but it also allows users to do the necessary in case of worst-case scenarios. Most programs also log system and UPS data as well as notify administrators via email and with alarms in case of a power failure. Older and high-end UPS devices typically still use serial ports for management, while all consumer-type and entry-level UPS products come with USB interfaces.