The power delivery subsystem is the internal circuitry in a PoE switch or injector that negotiates, regulates, and supplies electrical power to connected devices over Ethernet cables. It works alongside the data path, but it is a separate function: a port may still pass packets even if its power circuitry is degraded or disabled.
This matters in cyber security because many endpoints, such as IP cameras, wireless access points, VoIP phones, badge readers, and sensors, depend on PoE to stay online. If the power path fails, those devices can disappear without the switch looking fully down. Attackers may abuse that gap by cutting power, overloading ports, or forcing shutdowns to blind monitoring devices or disrupt building systems. Defenders watch PoE status, wattage draw, and per-port errors to spot failures, tampering, and hardware problems before they become outages.