As reported by engadget,
Apple first announced the new MagSafe product line during its October event, but the Duo didn’t become available for purchase until earlier this month. As its name implies, the $129 model can charge two devices at once. It even works with the Apple Watch, unlike the solo MagSafe charger, which doesn’t. Since it doesn’t ship with a power adapter, you can use your own — unless it’s Apple’s 29W model, apparently. The company recommends compatible 20W adapters for wireless charging up to 11W, though, or 27W adapters for wireless charging up to 14W.