Mikrotik is full of surprises

Have RB5009 (with poe on all ports) and Hap AX2
When RB5009 is connected with wall brick it work well and powers Hap AX2 which consumes about 5W

When I'm switching powering of RB5009 to PoE (which was my goal of being this device) it stops powering Hap AX2 with no valid psu message.

So my question is very simple: can RB5009 be powered over PoE and power other device at the same time?

So my question is very simple: can RB5009 be powered over PoE and power other device at the same time?

Pretty obviously it can't. And to me it's logical.

Pretty obviously

Would appreciate it if you’ll give a bit more details to me.
I just can not understand what is the problem to power 5W PoE device if RB5009 is powered by 70W brick over PoE injector.

Sorry for my stupid questions. I’m absolutely new in this area.

PoE 802.3 af/at/bt is all about standards. And if some device is "at" powered device (and agrees with power source device for maximum), it's limited to 25.5W at input (minimum required by standard) or 30W (maximum). RB5009UPr+S+IN consumes up to 15W on its own, so guaranteed power budget is somewhere between 10.5W and 15W. And that's not really enough to act as 802.3 af PSE.

And no, you can't go by "thumb rules" ... RB doesn't know that there's a 70W power adapter behind the PoE-in. The only effect of the over-dimensioned PA is that voltage doesn't drop as much when combined power draw gets higher.
And no, RB5009 up front from factory doesn't know that some crazy Ukrainian will only connect 802.3 at devices with power category 1 (up to 4W).

Further: high PoE currents also stress RJ45 connectors. And they are (I'm pretty sure) made to cope with up to 640mA (as implied by passive PoE-out spec), so you can't push those 70W (probably using 48V power adapter which means 1458mA).

So if I understand correctly good PoE splitter will do what RB5009 can not? If I'l just put splitter in front of RB5009 and power it with DC from splitter it will be able to provide power to other PoE devices?

Well, if your splitter ignores a few aspects of 802.3 PoE standards, then yes, it will do something that RB5009 doesn't.
But then the splitter you're talking about is likely passive PoE, so it doesn't care about power negotiation and all of that crap and just passes whatever power required and available. Just like the barel-type power connector.