Original Setup all running 7.5:
Main Router HEX S
* ether2 --> hAP ac^2 (using original power supply)
* ether3 --> hAP ac (using original power supply)
* ether5 --> hAP ac powered through POE

I upgraded my main router for an RB5009UPr+S+:
* ether2 --> hAP ac^2 (using original power supply)
* ether3 --> hAP ac (using original power supply)
* ether5 --> hAP ac getting error `poe-out status: voltage_too_high`

I am using the original power supplies when applicable.
I think the RB5009UPr+S+ is getting 48V from the brick power supply, and the hAP ac supports up to 57V (https://mikrotik.com/product/RB962UiGS-5HacT2HnT)

Did I miss anything? How can I get the POE setup properly?

Plug in a 24V power supply (it shipped with a 48v brick) and test. Your AP probably only accepts up to 28V. I saw the same error when I tried to plug a RB2011 into the RB5009 powered with the stock power supply.

Thank you, your suggestion worked.
I took the power supply from the hAP ac (24V 1200 mA) and connected it directly to the RB5009. Then the hAP ac is powered-on via POE...

I am still unable to poe other mikrotik devices using the original 48V. Even after upgrading to 7.6.

What are the downsides of powering the RB5009 with 24V instead of 48V? Any long term issues?

Downside of powering RB5009 with 24V instead of 48V is inability to use RB5009 as 802.3 af/at PSE. If your passive PoE clients would accept up to 48+V, then downside of using lower voltage is higher power loss on UTP cables (same wattage at lowed voltage means higher current, power loss in cable is proportional to current).

For RB5009 itself it may be actually benefitial ... DC-DC downconverters usually have (slightly) better efficiency when voltage difference between input and output is smaller (we're talking about small differences e.g. 93% vs. 95%). And every electronic device has a few DC-DC downconverters, electronic components these days run at voltages lower than 5V (sometimes lower than 2V). So as long as actual supply voltage (power adapters age and can drop volrage with time) falls inside acceptable range, device health should be fine in long term.

power loss in cable is proportional to current

No, it's proportional to current squared.

power loss in cable is proportional to current

No, it's proporional to current squared.

Which is still proportional, only not directly proportional.

Ok Thank you for your input @mkx!
I will update to 7.7 all my mikrotik devices when it becomes stable and will report back if the 48V finally works.

Ok Thank you for your input @mkx!
I will update to 7.7 all my mikrotik devices when it becomes stable and will report back if the 48V finally works.

It won't work ... SW version doesn't change the fact that hardware doesn't regulate voltage for PoEout ... hAP ac requires 8V-30V which 5009 can't provide if only powered with 48V.

Are you sure it is capped at 30V? I am under the impression that it can take 57V
https://mikrotik.com/product/RB962UiGS-5HacT2HnT

Are you sure it is capped at 30V? I am under the impression that it can take 57V

Ah, you're right, hAP ac can indeed take up to 57V.

Guesswork ahead ... There's another possibility as to why hAP ac doesn't power on if RB5009 is powered with 48V: RB5009 might only support 802.3 af/at PoE at high voltages (44+V) while hAP ac is passive (making PoE negotiation fail). ROS upgrade might change this or might not (I wouldn't bet on it).

Product brochure words PoE out as

PoE-Out: Same voltage as supplied, Passive PoE or 802.3af/at (requires 44.0–57.0 V input)

Also mentions "Smart PoE controller" ... which opens window for software bugs

I think this matter is ready to be escalated to official support ... either via support page or via e-mail (to support@mikrotik.com). When creating ticket, attach supout.rif file from RB5009 (while it can't power hAP ac) so that they can analyze the problem.

Will do!
Thanks so much for your insight!

Same issue. I was expecting it to be able to supply both passive 24 V and 48 V PoE - is this a hardware limitation?

Same problem here,

i tried forcing the voltage to high, and PoE to forced-on, but it said "PoE-overload".

So for me i solved it temporary with plugin two 24V PSU into the RB5009. So there is now enough power for the RB5009 and all the peripherals. And yes, i cut off the plug and connected it to the two pin connector.

It is a shame, that there is no DC/DC converter inside the RB5009.
Hey guys from Mikrotik, you hit the olymp with the RB5009UG+S+IN, but you messed up a meter before the goal with the RB5009UPr+S+.
I really hope, there will be something like an update Version, where there is an integrated DC/DC converter for the RB5009UPr+S+.