A post cap assembly for covering an upper end of a post is provided. The post cap assembly may include a post cap body having an internal post cavity that is sized and shaped to receive the upper end of the post and having a topper receiving aperture extending at least partially through the post cap body. An interchangeable topper may be positioned within the topper receiving aperture and projecting from the top side of the post cap body. Other post caps and related systems and methods are also provided.