If you have installed your WAX650S access point (AP) and recognize that the limited power is on, the likelihood is that it requires 802.3bt (max 60W) of PoE to ensure full power mode.

If the WAX650S uses IEEE 802.3af PoE or IEEE 802.3at PoE Plus, the limited power mode of it will be activated because the WAX650S requires 31 Watts to ensure the full power mode that enhances the throughput.

The LED lights could also indicate that it's in limited power mode:

Colour		Status	Description
	Amber	Steady On	The Zyxel Device is ready for use. The Zyxel Device's wireless interface is activated, and/or wireless clients are connected to the Zyxel Device in limited power mode.
	White	Steady On	The Zyxel Device's wireless interface is activated, but there are no wireless clients connected when it is in limited power mode.

What could happen if I force power mode? 

If the WAX650S is forcing the full power mode, the AP will use the PoE power that it needs, which means that it will utilize max throughput no matter if it has the PoE needed for it or not.

Note!
If the 802.11at can't deliver enough power for the WAX650S, then it could begin to restart itself.