Power control circuitry (i) applies an inline power signal from a power source to first and second terminals when a control signal delivered to the power control circuitry has an inline-power-ON value and (ii) shuts off the inline power signal from the power source to the first and second terminals when the control signal delivered to the power control circuitry has an inline-power-OFF value. Detection of an inline power shutoff failure includes obtaining a measurement signal from sensing circuitry while the control signal delivered to the power control circuitry has the inline-power-OFF value, and generating a result signal based on the measurement signal. The result signal indicates whether the power control circuitry is applying the inline power signal from the power source to the first and second terminals while the control signal delivered to the power control circuitry has the inline-power-OFF value due to an inline power shutoff failure.