Apple has updated its store listing for the still-unreleased MagSafe Duo charger with some more information on how the accessory will perform with various power adapters. As noted by Bloomberg’s Mark Gurman, the Duo charges at up to 11W with a 20W USB-C adapter, maxing out at 14W with an adapter that’s 27W or higher.

That means that when paired with Apple’s $19 20W adapter, the company’s cheapest option for USB-C charging, the MagSafe Duo can’t deliver as much power to the iPhone 12 as the 15W solo MagSafe charger. It also means that the fastest possible 14W option can’t match the regular MagSafe puck, either — and Apple’s best option for that will be the $49 30W adapter that’s packaged with the MacBook Air.

At $129, the MagSafe Duo was already going to be a pricey accessory that we wouldn’t recommend to most people. This latest information makes it seem even more niche, at a potential total cost of almost $180 to unlock its not particularly fast top speed. That said, it could still be a convenient, compact option for Apple Watch users who don’t want to bring along two separate chargers and cables when traveling.

The MagSafe Duo doesn’t have a release date yet; it’s listed as “coming soon.”