Please Note:

"The main purpose of a UPS is to provide backup power when the mains fail. International standards dont require UPS's to have surge protection so manufacturers are reluctant to build high level surge protetcion into the units as this will increase the cost and so make them uncompetitive. Therefore the UPS's need surge protection themselves.

Also, the load is unprotected from surges if an "Online" UPS is in bypass or when using a "Standby" UPS which will only have low level noise filtering/surge protection"

Standby UPS - (Small Business / Home Office)

An offline UPS provides battery power to equipment when the mains power supply falls below a pre-determined limit (usually around 200 V AC). This battery will usually last ten minutes. Offline UPS units are often referred to as standby systems, as the inverter is in standby mode until the mains power supply fails. They are inexpensive and recommended for home offices. Offline technology should be avoided for applications where there is frequent power disturbance.

Line Interactive UPS - (Corporate)

A line interactive UPS contains a regulator that boosts the mains power supply when it falls. It can regulate power to an acceptable level, without the use of a battery, during a brownout or surge in supply voltage. Similar to an offline UPS, there is a short period (ie transfer time) when a line interactive UPS will switch to battery mode during a blackout. Most line interactive UPS units have additional features including sinewave output, enhanced software and connectivity options. They provide a high level of protection, at an affordable price, for corporate applications.

Double Conversion / Online  UPS - (Corporate / Commercial / Industrial)

An on-line UPS absorbs the incoming AC supply, converts it to DC then inverts it to AC to supply critical power loads. An inverter supplies regulated AC power to loads at all times; either from rectified mains or a battery with an on-line UPS. In the event of a blackout, there is no transfer time or break in power supply. Most on-line UPS units contain an automatic bypass to ensure continuous power supply during a short-term overload or UPS failure. They are ideal for critical loads, sensitive equipment such as medical or scientific technology and industrial loads. All on-line UPS units are fully generator compatible.These UPS units are often referred to as double conversions because they can convert from AC–DC to DC–AC.