Power supply cover and mount for 2020 and sonoff

This is another power supply cover with additional space for sonoff to be included.
It can be mounted on the top of the corner brakcet of 2020 extrusion.
It was a little based on the tech2c cover from here https://www.thingiverse.com/thing:2084725 but mostly it's a new design for power supply to be mounted horizontally.