Re: Where does Origin download my DLCs? Attempting to transfer DLC content
@MamusiaTheCat When you install the base game through Steam, Origin installs your packs into the same place as all the Steam data. If you haven't changed the default install location in Steam, this is where the content would be:
Program Files (x86)\Steam\steamapps\common\The Sims 4
Each pack has its own folder inside that Sims 4 folder, and they're named by type of pack and release order. (For example, Snowy Escape was the tenth expansion released, so its folder is EP10.) It should therefore be easy to see whether Origin has downloaded all your packs.
It's not possible to add your Origin-bought packs to your Steam library.