Anet A8 PSU Bracket Corrected

I liked the minimal and efficient design, but I had some problems. The mounting holes to both the acrylic frame and the PSU were off, so I recreated the model in Fusion 360 with reference to Anet CAD files.

- Fixed acrylic mounting holes location
- Fixed PSU mounting holes location
- Added countersunk holes for short ATX screws
- Added extra support at the bottom