Devices that supply power when the commercial utility power system fails are called which of the following?

A.
power conditioners

B.
uninterruptible power supplies

C.
power filters

D.
power dividers

Explanation:
An uninterruptible power supply (UPS) is an electrical apparatus that provides emergency power to a load when
the input power source, typically mains power, fails. A UPS differs from an auxiliary or emergency power
system or standby generator in that it will provide near-instantaneous protection from input power interruptions,
by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery runtime of most
uninterruptible power sources is relatively short (often only a few minutes) but sufficient to start a standby power
source or properly shut down the protected equipment.
Incorrect Answers:A: A power conditioner is a device intended to improve the quality of the power that is delivered to electrical
equipment. It does not supply power when the commercial utility power system fails. Therefore, this answer is
incorrect.
C: A power filter is similar to a power conditioner in that it is intended to improve the quality of the power that is
delivered to electrical equipment. It does not supply power when the commercial utility power system fails.
Therefore, this answer is incorrect.
D: Power dividers are used in radio technology. They do not supply power when the commercial utility power
system fails. Therefore, this answer is incorrect.

https://en.wikipedia.org/wiki/Uninterruptible_power_supply