This article explains whether you can use a POE to power an Elo device while also connecting the DC power adapter and switching between them both

If you are using the Power over Ethernet (PoE) module to power your Elo device, do NOT connect the DC power adapter to the device.

Using both power inputs on the device can damage the internal power circuitry and render the device inoperable. Only use one or the other, but do not connect both at the same time.