A system and method for power sourcing equipment (PSE) detection of a powered device (PD) power failure for power backup. A PSE can power a PD at a low level of power as a backup power source. Upon a failure in the PDs primary power source, the PSE can detect a transient (e.g., current and/or voltage) on the PD load as a signal that the PD requires additional power. The PSE can then allocate increased power to the port by entering into an active state as compared to a backup state. As the PSE is responsive to the detection of the transient, the PSE need not rely on a real-time communication from the PD.