These are fan silencer shrouds for the Ender 3 and Ender 3 Pro power supply fans. They attach using the original screws that mount the fan to the inside of the power supply case. There are embossed and debossed versions with the Ender 3 logo and with just the Ender 3 dragon. There are versions for the Ender 3 and for the Ender 3 Pro with the Meanwell PSU.
IMPORTANT: Never have both screws removed at the same time or the fan will drop into the power supply case.
1) Remove one screw and attach the shroud with it. You may have to drill the holes to be a bit larger, so make sure the screw fits through both holes before attaching the shroud. You probably can do this by hand by just twisting the drill bit between your fingers.
2) Pivot the shroud out of the way and remove the second screw.
3) Pivot the shroud in place and secure it with the second screw.
Added V2 versions which are 1.5 mm shorter to accommodate newer versions of the PSU which have shorter screws. I left the original versions but there should be no reason to use them, although it's possible that they are better at silencing the noise. Pick one of the V2 versions to print unless you have a good reason for doing otherwise. Please let me know if the screw holes still aren't short enough in the V2 versions.
I also added versions for the Meanwell power supply where the shroud is mirrored on the Y-Axis, as well as V2 versions with no adornments for both PSUs. You could use one of the Ender 3 versions with the Meanwell PSU, but it would be blowing down instead of to the back of the printer. In the pictures, the Ender 3 shrouds are yellow and the Ender 3 Pro shrouds are purple.
Dual Colors with a Single Extruder
The embossed versions can be printed in two colors with a single extruder by pausing the printer after the shroud part has completed and then swapping in a spool of filament for the logo. You could do something similar with the debossed versions but it won't look as good. So if you're going to print with two colors, pick one of the embossed versions.
Most printers support the M600 G-code command, so you may be able to add in pauses using your slicer program. You may find the Colorprint tool useful if your printer supports the M600 command, but your slicer doesn't support adding pauses: https://www.prusaprinters.org/color-print/
If your printer doesn't support the M600 command, you will have to pause the print manually using the control panel immediately after the printer has completed printing the shroud part. This is at 18.28 mm for the V1 shroud and at 16.78 mm for the V2 shroud.
After switching filament colors, the nozzle may not be primed and the first bit printed may be under-extruded, so to compensate for this, I always add in a little cylindrical tower (10 mm diameter) and get the slicer to start the layers on that tower. For Cura, the settings that control this are Layer Start X and Layer Start Y, which are in the Travel section. I put the cylinder above the top right corner and set Layer Start X and Layer Start Y to a high number like 500. I've included a 19 mm tall filament swap tower in the download.
Note that the smoke coming out of the dragon's nostrils is only 0.27 mm wide in the logo versions, so if you're printing with a 0.4 mm nozzle the smoke won't be printed in the embossed logo version unless you turn on thin walls in Cura or use an equivalent setting in other slicers.
This is a remix of two remixes. I liked the addition of the logo in the Ender 3 PSU Fan Silencer Cover by Revolt64 remix to the Ender 3 Power supply fan silencer by Rohani_SousBois remix, but whatever process was used to modify the model made the surface look like it was whittled with a knife. So I've created another remix using the smooth mathematically pure shroud and the logo. Since both are remixes I also linked in the original Ender 3 Power Supply Fan Shroud by Mr_Clever_Coyote model as one of the sources for this remix. I also added versions with just the Ender 3 dragon.
I used FlashPrint to cut the logo from the one model and saved that as an STL mesh. I then used Blender's boolean modifier on the shroud to make a difference (debossed) and a union (embossed) with the logo.