How to feed the Poe port on MT devices with power from a USB charger, power bank, etc?
I’m not sure I understand your question fully but I would think devices powered by usb, will not be capable to feed POE to a subsequent device when that usb-source is used for power.
It’s only 5V and voltage convertors to step up, are not really power efficient so current goes up (I guess they can be had dirt cheap nowadays so cost is a lesser argument). You can do that externally, it’s not going to happen in the device.
There are devices with multiple power sources, once a source is used capable of feeding POE, it should be possible (provided the POE circuitry is present on that device).
E.g. mAP. Can be powered using usb, POE In and power brick.
When using usb, no POE.
When using POE In or power brick, POE out is possible.
So when you’re looking at that scenario, you need a power feed towards the device ready for POE voltages to be forwarded.
What scenario do you have in mind ?
”All USB-C cables must be able to carry a minimum of 3 A current (at 20 V, 60 W) but some can also carry high-power 5 A current (at 20 V, 100 W).”
POE 802.3 at/af requires (as far as I know) 48V (actually 44-57V).
So without a voltage convertor in the first device, that would be a problem. No ?
MT devices are made in such a way that POE voltage needs to be applied in order to feed to next device.
I have a hap ax2, it only has one PoE interface. I just want to power the hAP itself from my standard USB charging brick (4xA/2xC). Then I don’t need to carry the hAP’s own power unit. And more interestingly, I could also run it from a powerbank i.e. outside & mobile. Like the beach. 
Also many thunderbolt docks these days support 65W/95W onward PD so no reason a 100W powerbank couldn’t feed the laptop, and then the laptop power the hAP, etc. Or various other chained combinations.
Basically the hAP has just two input power possibilities - DC or PoE. I want to feed one of them from a USB source, I don’t really care which, just thought the PoE would be easier.
Ah, you want to use POE IN …
Spec AX2
PoE in Passive PoE
PoE in input Voltage 18-28 V
So you may have to carry a couple of car batteries connected in parallel to the beach 
And then RBGPOE, you still need to make the connection then to the batteries.
Whatever you choose, you need to comply to the input specifications for your device. Be it power plug or POE IN.
So you may also need a voltage convertor ?
For those purposes, a mAP or mAP Lite is perhaps more suited (at least it is more practical) ?
USB power in default.
You can set it to connect master wifi to your hotspot and then slave wifi to whatever.
Since I assume you want to share hotspot to broader audience ?
No, that is wrong! USB-C supplies can deliver a number of different voltages. They start out at 5V but they talk to a chip on the
receiving end that tells them what voltage to deliver.
So indeed it would be possible to add such an input to a (new) MikroTik device and have it powered by e.g. 18V directly from the supply.
This is also done by a laptop.
Yeah, I was too focused on USB in general. USB-C does allow more possibilities.
Some PoE Injectors accept Ethernet and DC power source (from 9V and up) and deliver some kind of PoE (passive 24V PoE, 48V PoE).
One such reference is TP-DCDC-1224.
I use one of these to power both a Raspberry and a WiFi AP using a single PowerBank.
I see that on Aliexpress you can buy cables with a USB-C connector at one end and a barrel jack on the other, claiming that they output 12V DC.
So likely there is such a chip built in to the USB-C connector that tells the supply to deliver 12V.
Assuming that your powerbank REALLY is USB-C PD compatible and indeed can independently deliver different voltages on each USB-C output (rather than just a dumb 5V type), you could use such a cable with the hAP AX2.
Familiarize yourself with the power capabilities of USB. The regular USB2.0 output guarantees a current of 500mA which provides 2.5 watts of power. The USB3.0 guarantees 900 mA which provides 4.5 watts of power. Standard USB3.2 output power of 7.5W. The higher wattage is only provided by devices that support the expansion standards. Notebook USB ports usually do not support them.
According to the specification AC2 consumes up to 16W.
So, you can power AC2 from an alternative USB power source only if this source supports the extension of the standard for PD power. To connect to such a device, you need to use PD adapters
https://www.conrad.com/p/joy-it-com-zy12pdn-converter-1-pcs-2475888
https://www.aliexpress.com/item/1005004657819372.html?spm=a2g0o.productlist.main.35.2ff041d8P0U2m5&algo_pvid=4dba619c-f5de-4c84-a602-23959d9b6810&algo_exp_id=4dba619c-f5de-4c84-a602-23959d9b6810-17&pdp_npi=3%40dis!GBP!1.01!0.73!!!!!%40214528be16862187634084376d076c!12000030004667281!sea!UK!0&curPageLogUid=6kVd1mjIlLbq
https://www.aliexpress.com/item/1005004904852980.html?spm=a2g0o.productlist.main.33.3eadUTZMUTZM4H&algo_pvid=ba8814d5-9378-4458-8e48-956a3e29f2ae&algo_exp_id=ba8814d5-9378-4458-8e48-956a3e29f2ae-16&pdp_npi=3%40dis!GBP!0.8!0.65!!!!!%402100bc5c16862192155125409d07ba!12000030969598485!sea!UK!0&curPageLogUid=gin8Pz1cli9I
OP asked about USB-C which is a different matter as explained in post #7.
Well my computer is using ~70W via USB 3.1 (“USB-C”) as write this. And new hAPax-lite uses USB-C already, so guessing more devices will add it over time.
I’ve used these things before:
https://www.balticnetworks.com/products/maxxwave-24v-usb-c-to-gigabit-passive-poe-ethernet-adapter
That provide 24V PoE from “USB-C” and act as a ethernet dongle, so pretty handy depending on the need.
“A device with a Type-C connector does not necessarily implement USB, USB Power Delivery, or any Alternate Mode: the Type-C connector is common to several technologies while mandating only a few of them.” https://en.wikipedia.org/wiki/USB-C
Many people are mistaken about the capabilities of the connector and the standard. The USB Type C connector can use the USB3.0 to USB4.0 standard. What capacities the version 3 standards provide I have pointed out. The higher powers are provided by the standard extensions such as USB Power Delivery, etc.
Some laptops can charge from a USB Type C connector with PD input, but I have not met any laptops that can power devices via USB with PD support.
Usually USB type C port in laptops provides 5V 1A power
That is certainly true. That is why I included that in the reply with the special cable.
The fact that he has a device with some USB-C charging outputs does not mean they can deliver 12V.
That is not entirely true.
Generally when people talk about usb-c they mean the usb-c standard, not just the connector. Fwiw, the usb-c connector is also used for Thunderbolt on the Mac.
There is no USB-C standard, there’s only UCB-C connector. Link you posted explains it all … https://en.wikipedia.org/wiki/USB-C
You know, I had a fight with someone in YT comments recently who tried to say that “USB-C 3.2 speed is 20mbps”. After I finished laughing I.. well I nothing, I’m still laughing.
But anyway I didn’t specifically ask about USB-C power capacities in relation to PoE, just only whether MT might be planning to add USB-C power options to their devices in future, as alternative to PoE.
Ok but 18V isn’t easy. 
I figured since the usual poe setup runs over generic cat-5/-6 cables it must be pretty lightweight and efficient. Guess not.
Well, NO! 
Besides the connector, there is the cable, signaling, voltage and power control and a whole lot of other stuff as well. Happy reading: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%20August%202019.pdf
AX Lite has USB-C connector for power input (5V) and nothing but that. mAP and mAP Lite have 5V micro-USB input.
It may (or not) come to other consumer oriented devices.
Higher voltages on POE are needed to reduce the current required to flow through those tiny cat-5/6 cables (lower current also means lower power loss because of resistance of those wires).