Now for sale on the Apple Store, the US$10 MagSafe 2 converter allows you to use the MagSafe connector on Cinema Displays (that includes the new Thunderbolt one as well) to charge your MagSafe 2-equipped MacBook Pro.

The new MagSafe 2 adapter offers a slimmer connector than the original MagSafe power port. You can pick up a standalone MagSafe 2 85W power adapter specific to the MacBook Pro Retina for $79 and a 45W MacBook Air model for the same price.

For comparison, here's an image of the two ports together, courtesy of Engadget