Buying Expansion Packs through steam (NEED HELP)

wat

Don't think you can do it. Steam's version is not going to add onto Origin's and vice-versa.

The only way this would work is if the keys are re-usable on Origin. Then you could use the key over there and add it to your Origin install. That's assuming you can do the gifting thing to get around not having the base game, which is not guaranteed either.

Best bet: wait for Origin to do another sale and but them there. They've been loosening up about sales, and they do have them from time to time now.

What's the point? xD

And I thought you could buy DLC for games you don't own anyways

Well if you can buy it but you can't look at the CD key you can always contact steam support and ask them for a way to view the CD keys for the DLC, so you can activate them/it on Origin.

Aren't the Sims 3 dlc cheaper on Origin anyways? If you want it on Origin it would make sense to buy it there.