I’ve purchased several of these four port passive POE injectors.
They have a center-positive barrel jack as well as a pluggable terminal block for input power connections. They are pretty handy for testing and temporary field deployments.
However, there is one shortcoming you’ll want to fix if you plan to use this in a permanent installation. Out of the box, there’s no provisions for bonding the shielded Ethernet jacks to ground. In fact, the two sides are not even connected to each other.
Ham Radio Mesh Networking 