Hi,
I’ve to replace some distribution switches with connected AX2/AX3/AC2/AC3 from their eth1 (poe-in@24V capable).
At this time, all theses HAP are powered by external PSU.
What happen if they are connected to switches that deliver poe-out@48V (standard)… ?
They’ll burn in fire ?
Yes, they might actually catch fire and surely there will be some smoke for you to admire. You need PoE step-down converter (in this very case from 48V to 24V) to use aforementioned devices with your 802.3af/at switch.
MikroTik does manufacture such device: https://mikrotik.com/product/rbgpoe_con_hp 
Thank you for your answer… so it’s less expansive to use dedicated non-poe switches for mkt devices and poe for the other devs
Hi.
No, relax.
“Proper / standards-compliant” 48V PoE (802.3af/at/bt) is doing negotiation.
If you plug in a device that does not explicitly “wants” this kind of PoE, there will be no power sent down the wire.
It is “passive PoE” which is very common among radio/WISP equipment (including many Mikrotik products), most commonly at 24V and very rarely at 48V, which is blindly-sent-down-the-wire and has a risk of damaging a device that is not expecting to receive it.
Plus, if your switch is programmable, basically always both kinds of PoE can be explicitly deactivated on a port, so you can do that if you want to feel safer.
Thank you, for your answer, i’ve still not choose furthers switches, i don’t know if i’ll buy mkt or other brand dev.