The power adaptor doesn't need any active ventilation. Please follow the following rules once installed into a wall niche:
The power adaptor should be installed in a dry environment where the operating ambient temperature might not exceed 40°C / 104°F.
Don´t position the power adaptor on top or on the back of the monitor system in order to prevent thermal overload.
The power adaptor should be adequately secured to prevent it from becoming unstable and/or falling.
Once the power adaptor is installed vertically the fan should be on the top.
When placing the power adaptor in a fully enclosed space, make sure the air flow around the sides and top of the power adaptor is not restricted. There should be a gap of at least 250mm all around the power adaptor.