An Ethernet power sourcing equipment (PSE), and a method and an apparatus for power over Ethernet (PoE), where the Ethernet PSE includes a PSE chip, a master control processor, a power supplying port, and a preprocessor. The preprocessor is configured to determine whether the master control processor starts upon power-on, control the PSE chip to detect whether the power supplying port is connected to a valid powered device (PD) when the master control processor starts upon power-on, and control, according to a preset rule, the PSE chip to power on the valid PD when the power supplying port is connected to the valid PD. Hence, the Ethernet PSE has abundant management functions and can quickly power on a PD.