Three different devices can be used to
protect sensitive computer equipment from the commonly occurring power
events:
Overall, the best solution for power events is having a
properly grounded building as well as enough battery power to run
all equipment in case of a power outage.
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– These can make sure that the voltage going to a device stays
below a certain level. These are mainly
used to stop spikes from zapping the hardware but also prevent
surges that are high enough in voltage to do damage. Surge
suppressors usually have a built-in fuse that stops excess amounts
of power from flowing through the unit. However, they are useless
during brownouts or blackouts. 
– These are equipped with a backup battery to supply power when
the incoming voltage drops below the normal level. The battery is on
standby during the normal operation of the unit. When the voltage slips, the battery kicks
in to provide DC power to a power inverter, which converts it to
AC power for the computer. The problem with this device is the
time it takes to switch over to the battery. If the switching
device fails, the battery will not be able to supply power to the
computer. 
– These are comparable to standby power supplies. However, a UPS
runs off the battery power the entire time it is in use. The power coming
into the unit recharges the batteries while they are in use. The
power from the battery is sent to an inverter, which sends AC to
the computer. The reason most people would choose to have a UPS
over an SPS is the switching time involved with an SPS. A UPS
gives a steady stream of power with no delay.