"Lenovo hasn't made it clear on the Tech Specs page (as of the time of this writing) that this is actually the correct adapter for the IdeaPad U systems, particularly the U300s. I was able to figure that out on my own (you have to search for the support page for this product). Then I put in an order, the adapter arrived, and just as I hoped, it was exactly identical to the one that came with the IdeaPad U300s.
I plugged it in and it works great. So if you own a U300s and want to buy a spare adapter, this is it."