Is there any router that can supply PoE? Please drop a mention even if it isn't supported by OWrt.
The Zyxel GS1900-8HP is a full 8 port switch that offers PoE on all ports, and that can be flashed to run OpenWrt (not sure how well PoE is integrated into OpenWrt, I bought mine for OpenWrt but keep running it under zyxel's OS, simply because for my simple needs that appears good enough.) In Germany these might be gotten second hand for 50-60 EUR it seems, new they tend to be well above 100EUR, not sure you consider even the second hand price cheapish enough?
A word of warning though, the zyxel can run OpenWrt and hence can also be configured as a full router, but the CPU really is nothing to write home about and will not be all that suited for modern internet access speeds (I think the charm of running OpenWrt on such a switch is to have a unified configuration interface between different network devices).
However you can buy a stand alone PoE injector for ~15EUR...
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IMHO, PoE on the Realtek-based switches on OpenWrt is working well enough: Ports can be configured to have a default "on" or "off" and can be switched on and off using a ubus call. The power budget can be configured and the current power draw can be displayed. There is no LuCI support for PoE management!
Keep in mind that there are also other PoE implementations for other devices, I can only speak about the Realtek switches.
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Injector price is right, but having gone for software NVR for only two IP cameras, whether injectors or PoE switches, the expense is going over the budget.
Router PoE would make sense because the upstream router can't bloody change the subnet mask, so besides having to power the cameras, an additional router is required, so I'm trying to see if we can bring cost down by combining. And I did find this Mikrotik RB750UPr2 (58.49 EUR), but no OWrt support.
EDIT Never mind, PoE out is passive as per the specs, so I'm guessing supplying power with adapter isn't going to get me any PoE...
Just an observation, I bought a PoE stand alone injector and an PoE splitter (to get the power back onto a barrel jack) to reotely power a DSL modem, but the PoE set-up introduced so much RF noise into the modem that the DSL sync suffered immensely so I switched back to using a local power supply. I guess IP cameras will be far more RF tolerant, but PoE power can be quite "dirty".
Isn't that because PoE splitters and injectors combo count as passive PoE, which is definitively incompatible with standards such 802.3af. I'm no expert in the matter—I haven't had the opportunity to mess around with PoE stuff—but AFAIU, client devices are supposed to negotiate the required voltage with PoE source, analogous to USB-PD.
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I would have guessed that on the wire active/passive would be the same. I selected an injector splitter pair that according to the data sheets should have matched (and it did, the modem did power up and operate just fine) it was just clear that the PoE power delivery massively interfered with the DSL signal...
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I'm just wondering if PoE negotiations are one-off or renegotiated later on as needed. Or maybe the splitter/injector pair was just not every good.
Anyhow, let me drag the topic back. I've no idea if used markets for such category of products exists here in this country, and the new MikroTik unit I found on Amazon was only FE, and passive PoE. The cheapest PoE 5-port switch I found is around ~25 EUR...
This is quite frustrating.
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Hm, I used to power my DSL modem with standard 802.3af for quite a while and I did not notice any degradation in the DSL sync (but my line isn't the best anyway, with a max of 45Mbit with vectoring).
I can't see a reason why the PoE power itself, i.e. DC power, would influence the DSL line. Maybe the quality of the regulator used in your PoE extractor was that bad?
Just yesterday I learned about the Aerohive BR200-WP router. It is a router with 5x Gbit and 2x PoE, and it is supported by OpenWrt. BUT: The PoE management isn't supported at the moment. See here: Bringing support for realtek-poe to mainline OpenWrt - #183 by MrGangster
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Doesn't look like it's an option. Google shopping tab only shows Ebay (international; no local Ebay market AFAICT), and nothing on Amazon.
Even if I forget the budget, I can't find any option. EdgeRouter X only as a single PoE port, and I think there was a now discontinued EdgeRouter PoE 5-port. Can't find the latter for sale anywhere save for international Ebay again.
As with all psu there are two kinds. The cheap ones and the expensive ones. On the outside they look the same and they do the same “work” inside the electrical DC specs.
But on every cheap PSU I have opened the PCB location where the filters and safety devices are supposed to be mounted are always empty and bypassed.
The thing is that such a device would be illegal to import to EU for example and sell but people and some companies buy these devices online and import them under the radar to cut cost.
If the psu unit doesn’t have a meaningful manufacturer homepage with a meaningful datasheet that actually mentions noise and isolation and tolerances. Well then you know what the hardware quality is.
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This leads to am off-topic follow-up question:
Is there a reputable source for PoE splitters?
My bet is that between the ubiquity injector and the no-name splitter from amazon, likely the splitter is sub-optimal...
I am using TP-Link splitters to power a Philips HUE hub.
Have also used that model to stress test PoE ports.
But if you use brands like TP-Link, Ubi etc I would be really surprised if you run in to EMI problems since that would mean a economic impact on their products which are on business in this product category.
But emi can come from the ethernet cable in use also.
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Speaking of which, I know shielded cables protects signal from EMI, but does that also prevent EMI from the shielded cable itself?
Shield works in both ways. But the subject is more complicated than that. For higher speed the four wire pairs are twinned pair-wise but with different rotation gradient between the four pairs. That is because the transmission potential is free floating from ground and is differentiated. The result of that design is that the residual current and offset voltage in the loop is zero so no magnetic transmission will occur. That is why you can’t measure anything with a multimeter on a ethernet cable, you need a ethernet transformer at the endpoints to get the actual data signal.
On top of that with cat6 cables you can have screens both on wire pairs and around the whole cable. But conducting screens can make things better or worse mostly depending if you get ground current loops through the screen.
But the general rule in emi is to stop the transmission and not to fix the receiver.
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You local Planet pusher, maybe? But it comes with a price tag...
FWIW, I have a couple of really cheap no-name 12V splitters I bought on eBay (or AliExpress?) a few years ago, which so far have worked flawlessly. A few months ago I tried to buy a few more. Searched both sites trying to eliminate all the bad copies. And finally decided on a model which looked exactly like the ones I had, with matching specifications in the ad text.
The first thing I noticed when unpacking was the 4 missing wires in the RJ45 plug. So much for the "gigabit" spec....
No problem getting a refund. But I'd much rather be able to buy a working product. That's not an option anymore, it seems.
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I recommend going for the router + switch solution, simply because there are infinitely more alternatives. Routers with PoE PSE capabilities are so rare that you're bound to end up with all sorts of compromises in other areas.
A PoE switch will be more expensive than a PoE injector if you only need a single port. But you do get some nice additional features: power metering and control. Being able to remotely cut power to a device is very useful. And monitoring consumption can aid in debugging. I've had access points crashing where I could see the radio was powered down simply by looking at the switch statistics (AP using 2W instead of the expected 5+W)
And when you first have one PoE powered device you'll want more. Better buy a switch from the start 
I am very happy with my two ZyXEL GS1900-10HPs running OpenWrt. These are similar to the already recommended 8HP, only with two additional SFP ports. But I understand that the PoE management protocol of the current variant isn't supported yet. So I can only recommend the first version.
I'm also happy with the Cisco C3560CX-12PD-S I'm using as my main PoE switch at home, even if it doesn't run OpenWrt. It has a really stable and nice vendor firmware. The main advantages over the ZyXEL switches are more ports, internal PSU and two 10gig ports, still without a fan. But not exactly cheap....
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I second that. I got my PoE switches all for cheap on the used market. The ZyXEL GS1900-24HP is my main PoE switch, the D-Link DGS-1210-28MP is the backup. I only need VLAN and PoE configuration anyway, so their performance is more than sufficient.
I've also added quite some more PoE devices since I got them, it's really convenient.
I do recognize the wisdom here, but it's not my network, I'm actually setting up a small LAN for someone else, and all those of quality of life features are going to end up unused.
Let med describe the situation a bit here. The owner is setting up a crypto mining farm, but on the small side, it's going to be like around 40-ish devices. IDK why, but they've chosen to go for a mobile network connection, i.e. mobile network provided SIM and router. First problem is here, because this stupid Oppo router doesn't let you set subnet masks, which I have to configure so they can have everything in 192.168.0.1/16 so as to categorize same types of devices with x.1, x.2, second type on y.1, y.2 and so on. This is why a secondary router is needed, purely for a subnet.
Second is the cameras, and this is where PoE comes in. There's going to be a grand total of two cameras, one overlooking the machines, the other the cooling/ventilation system. There's no dedicated NVR here. They gave me a laptop where I installed VPN and the NVR (Agent DVR—not sure why its called "DVR" or even if it's any good, first time dealing with an NVR solution), and so far cameras have been configured properly with power adapter, but that's not going to cut it for wall mount.
Because of the limited applicability of either the router and PoE, I am very reluctant to splurge at all. Once this has been set up, I'm out. The quality of life afforded by dedicated hardware means nothing to me, or whoever going to oversee this place because they've close to nothing in terms of IT know-how.
PS The devices are connected via a 48-port D-Link managed switch, which I went over another thread. For some God awful reason, any GbE unamanged 48-port switch I found were for some reason around the same price as the managed or more. This switch may or may not be supported by OWrt (the revision is suspect, as is D-Link firmware's penchant to accept only encrypted firmware), but it's not in consideration for secondary router because it's not a router.
Thus far, I'm feeling partial to a MikroTik hEX router than has 4-port PoE out. I'm still waiting to know the price—will likely go for this if price is reasonable.
Unfortunately, the hEX series thing doesn't seem supported in OWrt.