Odyssey G5 PSU under desk holder.

No supports are necessary, however you may improve surface quality of the overhang between the screw mounting points if you decide to use supports there. (Printed without supports in the photos) As for the rest of the overhangs I see no point in using supports there.

Screw holes are 4mm in diameter (for 3mm screws) and the hole for the screw head is 9.4mm in diameter (you can choose what screws you would like to use based on these diameters)