Ender 3 original black plastic PSU cover is compatible with Mean Well LRS-350-24, but it leaves a 20mm gap between the cover and the PSU case. You can either print a new cover from scratch, or save time and filament and print the inset to close the gap.
The original design (https://www.thingiverse.com/thing:4117645/) seems to have an error: the screw hole does not align with the screw hole on the Ender 3 black plastic PSU cover. This rework fixes this issue.
psu_cover.stl | 38.8KB |