An Offline UPS (also known as Standby or Voltage and Frequency Dependent) is the simplest and least expensive UPS type. An Offline UPS is suitable for protecting against power outages affecting non-critical electronics such as PCs, peripherals, and office equipment, as well as home entertainment devices like TVs and gaming consoles. Essentially, this form of UPS will send power directly from the mains to the device’s power source until a power outage occurs. In the event of a power outage, the UPS will switch to using its internal battery to power the connected devices.

The greatest disadvantage of this sort of power source is that it does not immediately switch to battery power until it detects a power loss. This could result in the failure of the equipment linked to the power source. Most offline UPS systems lack the characteristics necessary to reduce surges and prevent equipment damage.

A Line Interactive UPS (also known as Voltage Independent) provides greater protection than an Offline UPS. With a Line Interactive UPS, mains power flows into an Inverter/Converter. The energy is then separated into AC and DC currents. The DC charges the battery of the UPS unit, while the AC flows to the equipment’s power supply. When there is a loss of power to the mains, the equipment is powered solely by the UPS battery.

A Line Interactive UPS still has transfer time when the power goes out, but it responds more quickly than Offline variants. In addition, a Line Interactive UPS unit will filter the AC flowing from the mains through the inverter and smooth out any mains power fluctuations that could harm your computer.

An Online UPS system (commonly referred to as a Double Conversion UPS) provides the superior power protection that critical and sensitive equipment needs. In an Online UPS solution, the battery provides power, and the power from the mains is constantly used to recharge the battery.

Comparable to using a laptop while plugged in. In case of a power outage, the device will continue to run until the battery dies.

In the event of a power outage, there is no transfer time when using an Online UPS system. However, and probably even more crucially, by routing all mains power through the battery, there is an additional level of safety against any voltage spikes or decreases. Surges and voltage drops can potentially cause harm to electrical equipment and computer systems.

Often, Online UPS solutions are only available with significant output power capacities. Although they can be more expensive than Offline or Line Interactive UPS systems, they can provide significant energy savings for large units and a higher level of safety overall.