Power outages occur when power simply drops out, which is typically described as having a duration of more than half a cycle so that no voltage is being applied to an electrical or electronic device. This could be the result of a ground fault equipment failure or a power company transformer that fails for some reason, therefore, failing to provide power efficiently into a building, home, or other type of facility.
If your main concern is power outages, which should always be a concern when it comes to access control, but even in other critical components that utilize low-voltage, you always want to make sure you are incorporating a UPS (Uninterruptable Power Supply). These scenarios are typical types of situations in which a UPS is beneficial to keep equipment powered for an extended period until the equipment can be powered down safely or to preserve the integrity and access control security of the facility.
You may also refer to the following Power Management video for additional overview information about power.