The TP-POE-HP-48GDX2 is a unique high power PoE  injectors with Dual 802.3af/at compatible outputs. This means that two devices  can be powered from a single PoE injector. The data path between the devices is  handled by the injector so no PoE switch is required. 
There are models that will run on 12VDC or 24VDC as well as  110/220VAC grid power. The different models have different total combined  outputs up to 70W. 
They have two DC inputs for connecting 2 power sources, like a  primary and backup power source. They have various protections for short circuit,  overload and surges caused by ESD or lightning. The built-in surge protection  protects sensitive connected devices from damage due to surges on data and PoE  lines. All 8 wires are protected. The input voltage and output voltage are  isolated to avoid any grounding or negative voltage issues.