If you do not supply the Cloud Key via PoE, then you need a power supply unit that supplies at least QC 2.0 or better. This is stated in the manual and has already been answered in this way in another question. Or you can get yourself a PoE injector, such as this one: Ubiquiti PoE Injector (PoE Injector)
And then it fits perfectly.

With the enclosed power supply unit, it says the power supply is too weak? Then I would think there is something wrong with the power supply unit. Sounds like a defect to me. Should I exchange it?