It is very nice to have a backup power generator for those occasions when there is a power outage. This is particularly so in South Africa, where the national power provider has proven to be so unreliable in the near past. However, there is an added danger of using computers with a backup generator, and great care should be taken when using computers or other delicate equipment. The voltage and frequency of the power produced by a generator depends on the engine speed, and the speed is controlled by a governor. Some governors are mechanical, some are electronic. The job of the governor is to keep the voltage and frequency constant as the load changes. However, there is no guarantee that the voltage will remain constant, and you should avoid using a computer with a standby generator if at all possible.

There are several common power problems that a UPS can correct:
· Power failure — Total loss of utility power, with possibility of severe transient conditions upon failure and/or restoration: Causes electrical equipment to stop working (transients may cause permanent damage).
· Voltage sag – Transient (short term) under-voltage: Causes flickering of lights.
· Voltage spike – Transient (short term) over-voltage i.e. spike or peak: Causes wear or acute damage to electronic equipment.
· Under-voltage – Low line voltage for an extended period of time: Causes overheating in motors.
· Over-voltage – Increased voltage for an extended period of time: Causes light bulbs to burnout.
· Line noise – Distortions superimposed on the power waveform: Causes electromagnetic interference.
· Frequency variation – Deviation from the nominal frequency (50 or 60 Hz): Causes motors to increase or decrease speed and line-driven clocks and timing devices to gain or lose time.
· Switching transient – Instantaneous undervoltage (notch) in the range of milliseconds to seconds: May cause erratic behavior in some equipment, memory loss, data error, data loss and component stress.
· Harmonic distortion – Multiples of power frequency superimposed on the power waveform: Causes excess heating in wiring and fuses.