[edit] Offline / standby Offline / standby UPS. Typical protection time: 0 - 20 minutes. Capacity expansion: Usually not availableThe Offline / Standby UPS (SPS) offers only the most basic features, providing surge protection and battery backup. With this type of UPS, a user&＃039;s equipment is normally connected directly to incoming utility power with the same voltage transient clamping devices used in a common surge protected plug strip connected across the power line. When the incoming utility voltage falls below a predetermined level the SPS turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. The SPS then mechanically switches the connected equipment on to its DC-AC inverter output. The switchover time can be as long as 25 milliseconds depending on the amount of time it takes the Standby UPS to detect the lost utility voltage. Generally speaking, dependent on the size of UPS connected load and the sensitivity of the connected equipment to voltage variation, the UPS will be designed and/or offered (specification wise) to cover certain ranges of equipment, ***** Personal Computer, without any obvious dip or brownout to that device. [edit] Line-interactive Line-Interactive UPS. Typical protection time: 5 - 30 minutes. Capacity expansion: Several hoursThe Line-Interactive UPS is similar in operation to a Standby UPS, but with the addition of a multi-tap variable-voltage autotransformer. This is a special type of electrical transformer that can add or subtract powered coils of wire, thereby increasing or decreasing the magnetic field and the output voltage of the transformer. This type of UPS is able to tolerate continuous undervoltage brownouts and overvoltage surges without consuming the limited reserve battery power. It instead compensates by auto-selecting different power taps on the autotransformer. Changing the autotransformer tap can cause a very brief output power disruption, so the UPS may chirp for a m