@ErniePantuso 

Hey

In short any good quality POE injector that meets the 802.3af specification should work perfectly for you, I have used Ubiquiti and Maraki POE injectors interchangbley with Omada for a long time now.

In terms of distance and placement, the Injector needs to be the last device before the AP (between switch and AP), distance wise most injectors are good for 80 meters (~350 feet).  You can push 100 meters, with good quality cat6 cable if needed.  

For your 50 meters, near the switch is fine!

  @ErniePantuso 

In your case (EAP225 V2), any 802.3af-compliant injector should do. However, the "TL-POE170S is incompatible with EAP235, EAP225, and EAP225-Outdoor. To power up these EAPs, TL-POE160S is recommended to use." (source).

TP-Link has a FAQ which also discusses cable length here: https://www.tp-link.com/no/support/faq/906/ - as long as you use good quality copper cabling, you should be fine.

However (and this is also mentioned in the linked FAQ), this does not apply to TP-Link EAPs that come with a passive PoE injector (such as the EAP225 V3) - while it says they are 802.3af-compliant, they only accept one of two possible PoE wiring pinouts (mode B according to the FAQ). PoE power sourcing equipment (PSE) such as an injector or a PoE switch can be either mode A or mode B (or have different pinouts on different ports), and powered devices (PD) must accept both pinouts according to the standard. However this is not the case for "hybrid" devices from TP-Link (and other suppliers) - so you need to make sure your power sourcing equipment provides the required mode.  Don't ask how I found out about the different modes :).