This is a Decora-style electrical outlet cover plate. The design has been optimized for 3D printing on an FDM printer, so its design varies slightly from the versions available for purchase.

PRINT INSTRUCTIONS: Orient the plate face down on the print surface. Use infill density of 20%-30% for a strong cover, an infill of 10% will work if the cover is on a rarely used outlet. Us 3 or 4 outer walls. No supports are needed.