According to the U6-LR Data Sheet - leaving alonw the passive non-standard variant - the U6-LR is requiring a PoE+ (802.3at) PSE - these 16.5W not much above, but it's not sufficient.
Both the GS108PEv3 as well as the GS105PE offer PoE (802.3af) PSE on the ports. Either way, this is max 16.4 at the PSE, and max 15.4W per port on the PD - so definitively not sufficient to power a PoE+ device like the U6-LR - that's why there is a Power Fault: The AP does request more than the GS108PEv3 can supply on a port.
The information on the GS105PE says: PoE pass-thru: 19W with 802.3at/7.9W with 802.3af input power. If powering from a PoE+ 802.3at PSE, the power limit for both PoE 802.3af ports is a total of max. 19W - this does not allow the first 802.3af PoE port to supply more than these 16.4 W at the PSE, resp. max 15.4W at the PD - and it still does signal (all IEEE standard PoE-versions work strictly on wht is negotiated on the PoE "link"). Here again, the AP does request more than the GS108PEv3 can supply on a port - thus agin a Power Fault.
It's not about what the teachers told us on the intro to electricity - IEEE PoE-versions are much smarter. The AP does request Class 4 PoE+, but the switch has only max Class 3 (or Class 0, the default unspecified variant) PoE available on the port.
Awesome! Thanks for the answer and explanation! Only one thing is that GS108PEv3 does power fine the U6-LR, I have no issue when powering direct, but certanly have with the GS105PE in the middle
Only one thing is that GS108PEv3 does power fine the U6-LR, I have no issue when powering direct, ...
This is more a side-effect than a true intention. But I can note the Netgear WAX620 for example does allow the same why ever. Strictly to the specs this should not work - and some limitations like reduced output power/reach for example (or worst case unintended reboots under full load) can apply.
... but certanly have with the GS105PE in the middle
With just a PoE 802.3af PSE port supplying power to the GS105PE, only one PoE port will be useable, the max negoteateable output power (just one one port) is a 802.3af Class 1 (4.4W at the PSE) or Class 2 (7.6W at the PSE) .
You might want to try a PoE+ 802.3at power source for the GS105PE instead.
