When the equipment is switched off, the extra voltage is dissipated through the power line. Computers and other sensitive electronic devices are designed to receive power within a certain voltage range. Electrical noise disrupts the smooth sine wave usually expected from utility power. Electrical noise is caused by many factors and phenomena, including lightning, load switching, generators, radio transmitters, and industrial equipment. It can be intermittent or chronic.
Noise introduces glitches and errors into executable programs and data files.
Only a battery backup provides this type of power protection.