Electric utility companies do not need to provide your building computer level of power supply, and they usually don't provide!
Long been overrun condition may damage equipment and shorten IT equipment life. Utility power supply often power surge, voltage sag, electrical noise, harmonic, load fluctuations and other distractions. With a standard utility power supply business customers of these abnormal power supply problems every day, every year will have 4 to 15 complete power interruption. Even a brief power interference, can also cause lead to hours of downtime events.
UPS power supply will be by adjusting the input power to mitigate voltage sag and jump, and provide the battery backup power to prevent voltage sag and complete power interruption, to prevent the above problems.