An exemplary powered device (PD) connected to a local power source and a power sourcing equipment (PSE) includes a constant current source drawing at least 10 mA direct current from the PSE when the local power source is in operation. The PD includes a first conversion circuit, a first diode, and a second diode. The first conversion circuit comprises a first input and is configured for converting a voltage input to the first input into the rated working voltage of the PD. The positive terminal of the first diode is connected to the local power source and the negative terminal thereof is connected to the first input. The voltage of the local power source is higher than that of the PSE.