If your Cisco switch PoE is not working, the most common causes are an exhausted PoE power budget, a disabled inline power configuration, physical cable faults, incompatible powered devices (PD), or a crashed PoE controller. To isolate the problem fast, log into the Catalyst switch and run show. Power over Ethernet (PoE) simplifies device deployment by delivering both data and power over a single Ethernet cable. However, when PoE fails, it can disable critical infrastructure like IP phones, wireless access points, and security cameras. Here are some common PoE issues and how to troubleshoot them: 1. This can also happen if one of the power supplies suddenly fails.