Unifi Switch Flex setup and documentation
I really like Unifi's networking gear. I have a Dream Machine Pro, a half dozen of their access points, and just bought my first switch from them, the UniFi Switch Flex 5-Port Managed Gigabit PoE - it's perfect for connecting my access points and security cameras to my main network.
For my use case, I have to mount the switch outside, which meant I had to also buy a weatherproof Unifi Switch Flex Utility box - so far so good.
When the packages arrived I opened the boxes in my office and much to my surprise, although the Switch Flex Utility includes a PoE adapter, it doesn't contain an A/C plug!! 
I had to cut apart a power cord I had laying around, strip the insulation off the ends...
and wire the PoE adapter myself.
Needless to say this was unexpected, not documented, and a big inconvenience.
I got the box mounted, plugged in my new PoE adapter and all my devices, adopted the new switch through my Dream Machine Pro, and more fun awaited me - my security cameras and access points were endlessly power cycling! So frustrating. I looked for loose or shorted connections but couldn't find anything wrong.
Then I did what any self-respecting nerd would do: I searched the internet for "Unifi Switch Flex power cycling" and discovered the solution: For some inexplicable reason, the Switch Flex has to be manually configured to work in PoE mode! What??!
Here are the steps (I used the web interface):
- In your Controller (Dream Machine Pro, Dream Machine, or other) choose the Flex switch (Devices / Flex) and Choose "Settings"
- Choose "Services", and expand this section of the menu.
- SCROLL DOWN to Power Source, select PoE Injector
- Click Apply Changes.
Now your PoE devices will be happy, you'll be happy, and Unifi will owe me a debt of gratitude for documenting this ordeal!
Enjoy.