Standby UPS (Offline UPS):

Standby UPSs allow equipment to run off utility power until the UPS detects a problem, at which point it switches to battery power to protect against sags, surges or outages. This topology is best suited for applications requiring simple backup or with less sensitive equipment, such as small office/home office and point-of-sale equipment.

Line-Interactive UPS:

Line-interactive UPSs actively regulate voltage either by boosting or decreasing utility power as necessary before allowing it to pass to the protected equipment or by resorting to battery power. Line-interactive models are ideal for applications where protection from power anomalies is required, but the utility power is relatively clean. Main distribution frame (MDF) and intermediate distribution frame (IDF) communication closets, non-centralized server and network rooms, and general IT enclosures are ideally suited for this topology.

Online (Double-Conversion) UPS:

Online UPSs provide the highest level of protection by isolating equipment from raw utility power—converting power from AC to DC and back to AC. Unlike other topologies, this double conversion method provides zero transfer time to battery for sensitive equipment since the electricity is already coming from the UPS. The online, double conversion UPS topology is best applied to mission-critical equipment and locations where utility power is poor or highly unreliable.

Ferroresonant UPS:

Ferroresonant UPSs operate similarly to line-interactive UPSs with the exception that a ferroresonant transformer is used to condition the output and hold energy long enough to cover the time between switching from line power to battery power which effectively means a no-break transfer. Many ferroresonant UPSs are 82-88 percent efficient and offer excellent isolation. Although no longer the dominant type of UPS, these robust units are still used in industrial settings such as the oil and gas, petrochemical, chemical, utility and heavy industry markets.

Multi-mode UPS:

Multi-mode UPSs are considered the best choice for companies looking to achieve an optimal balance of efficiency and protection. The two modes within these UPSs are a high-efficiency, eco-mode and a premium power protection mode. The UPS can switch between these two modes automatically when it detects problems in the utility power. This functionality can save a significant amount in operating expenses.