Since you mention uploading files, you'd want to use Photoshop Exchange. Photoshop Marketplace relies on the 'publisher' to serve the files and doesn't have an upload feature. I'm not involved with this project so I certainly could be wrong on this point, but I don't think one is meant to replace the other.
Photoshop Exchange has historically been a place to find files that can be directly uploaded/downloaded which extend the capabilities of the Photoshop application. Marketplace is a newer service that has a broader goal to provide information related to Photoshop solutions which includes information about books, DVD's, events, user groups, as well as the types of files distributed in Photoshop Exchange.
Hopefully that helps clear things up a bit.