Can you try powering the RB3011 with a 24VDC 2A PSU instead. My feeling is that the power supplied by the 24VDC 1.2A PSU is not enough to power the RB3011 itself and then the external device on port 10. Note that the 24VDC 1.2A PSU may not have 100% efficiency therefore the total output power should be reasonably below 24x1.2Watts (28.8W). 3011 alone consumes about 10W. Some power will also be lost on the poe cable etc. To be sure, connect a low power device to the port 10 (Such as hAP or mAP which is 3.5W) and see if it comes ON or not.Same issue again here.
RB3011 straight out of the box, will not power anything with POE port 10.
Tried forced on and nothing works.
If there is any means to check the power consumed by the SXT, in question and compare it with a new SXT, that will be nice. You might be surprised to find out that it takes more power than the router can support.I have solved issue by replacing the SXT unit powered by 3011
Note that "suspected faulty" SXT is OK with its own injector, and powers up OK with few 3011 but KO with other 3011 units.
It seems an edge situation where , anyway, 3011 PoE capability is at its limit.
Unfortunately I can try no more that case with an higher current power supply....