Teltonika (& many other suppliers) often don't explain well what they mean by PoE creating confusion. Mainly around the use of the term "PoE", ie in a "generic sense" vs PoE in the official sense ie to the 802.3at/af IEEE standards. Further, there is also a need to explain if a device provides power or needs power. For example, an Ethernet Switch such as TSW-100 is technically referred to as PoE-PSE (Power Sourcing Equipment) ie it supplies PoE Power to PD's. And a device that accepts PoE Power from a switch or Injector is called a PoE-PD (Powered Device), such as VoIP telephones, IP Cameras and some routers. Not using the correct suffix leaves the question open as to what is the device can do. be aware that TSW-100 will require external 48V dc Power in order for it to work as PoE-PSE to the standard. If you power it with a lower voltage eg 12V it may still supply power but no longer the PoE standard - but will work to the Passive mode.
Passive PoE, the type of PoE that is supported on some of the Teltonika devices, is non-standard ie a proprietary version of PoE...So a TRB140 is sort of a PoE-PD but not to the standard. Passive PoE just means that the spare pairs (4,7 & 5,8) in the RJ45/CAT5/6 connector can be used for getting DC power into the device and pins internally are wired in parallel with the external DC supply pins so you have the option of supplying the same dc power via either RJ45 or external connector or potentially both. The actual voltage will vary with each device type, eg the TRB 140 can have 9-24Vdc on those pins see following; https://wiki.teltonika-networks.com/view/TRB140_Powering_Options
PoE (802.3at,etc) works on sending 48V on those same unused pairs. Passive operating voltages can be random and will vary with each OEM.
PoE Switches and Injectors can often do other clever stuff like detecting if the PoE-PD device supports PoE at all - if it detects it doesn't then it won't supply power thus preventing potential damage to the device. More sophisticated PSE (typically on a managed ethernet switch) can turn the power on and off remotely to a specific port which can be very handy to do reboots tec.
Hope this helps.
We often make up a 3-way cable that splits out DC Power Feed and Comms at one end and the regular RJ45 at the other that connects to the TRB's saving the need for running extra dc power cable.