Let's take these three devices:
A = switch RB260GSP, PoE IN on port 1, PoE OUT on ports 2-5
B = access point cAP AC, PoE IN on port 1, PoE OUT on port 2
C = router hEX, PoE IN on port 1

Legend:
A.2 = device A, port 2
--- = network cable

I powered A with its power supply but through a PoE adapter (RBGPOE) and a 3 meter network cable. Then I powered B and C by connecting them to ports A.2 and A.3 and everything works.
Changing only the 3 meter cable with one of about 25 meters here is what happens:
Basically, if A is powered with its power supply via PoE but with a 25m cable, C does not turn on if connected directly, eg. to A.2
By simply putting B between the two, C turns on and runs smoothly.

Can anyone give me an explanation?
("It makes no sense" answers are also welcome ;-)

Regards.

RB260GSP SwOS version?

SwOS 2.13

I not understand the problem,
you try to force poe out on right ports?

I don['t think You can use the RB260 PoE out while powering it through PoE. To really use its four PoE outputs You would need run it through the DC in jack.

test 4) A.2---B.1 + B.2---C.1 = A, B & C on

this works,

and with 3m cable works.

I not understand the problem,
you try to force poe out on right ports?

Yes and nothing changes.

I don['t think You can use the RB260 PoE out while powering it through PoE. To really use its four PoE outputs You would need run it through the DC in jack.

I absolutely confirm, the RB260 is powered by its power supply but through a PoE Y adapter, precisely the one supplied with the cAP AC unit and a 25m cable. Under these conditions the "test 4" configuration works and I'm looking at it right now ;-)

test 4) A.2---B.1 + B.2---C.1 = A, B & C on

this works,

and with 3m cable works.

Yes "test 4" works, both with the 3 meter cable and with the 25 one.
The strange thing is that with the 25 meter cable, and only with that, "test 2" and "test 3" do not work, at least with the units I have in my hand ... I tried and tried again and when I saw instead that " test 4 "it worked I could not believe my eyes and I died laughing!

It almost seems that cAP AC works as an "amplifier" ...

Again, I accept answers like "it's inexplicable" and I sleep peacefully anyway.
Good evening everybody.

The only possible cause is... drop voltage.
Ethernet cable are really tiny and 25m can cause little undervoltage.

cAP and hEX have different needs, probably the poe circuit think than cAP use less power.

And cAP ac probably have less problem and power the hex without problem

I don['t think You can use the RB260 PoE out while powering it through PoE. To really use its four PoE outputs You would need run it through the DC in jack.

I absolutely confirm, the RB260 is powered by its power supply but through a PoE Y adapter, precisely the one supplied with the cAP AC unit and a 25m cable. Under these conditions the "test 4" configuration works and I'm looking at it right now ;-)

Again, I accept answers like "it's inexplicable" and I sleep peacefully anyway.
Good evening everybody.

If You are using a PoE injector, then the unit is powered through PoE. The problem is the power limits of the ETH1 (I think). Try connecting the power supply direct in the unit - bypass the ETH1 in the process.

I have one of these RB260 with PoE. Now I'm powering one hEX and one ACLite. I have already powered one hEX, one ACLite and one hAP AC2. But I have the power supply directly connected to the DC input.

The specs only list max amps out per port. Perhaps that same limit is for Poe in port?

The cap has different hardware and might be able to sense the correct amps on the Poe out vs the rb260.