Image credit: Apple
There is now a dizzying array of power adapters, wattages, Magsafe connectors (original and version 2) and connector types ("L" and "T" shapes) that go with each MacBook Air and Pro model. John Martellaro helps sort it all out.
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Apple has provided an impressive tech note, HT201700, that tells you how to match your MacBook Pro or Air to the right connector and power adapter. Of course, as we know, the new 2015 MacBook uses its own 29 watt power adapter and USB-C connector, so that one is a one-of-a-kind no-brainer for now.
For the MacBook Pro and MacBook Air, the first step is to determine your model and year. That information can be found in OS X under the Apple menu > About This Mac.
The next step is to refer to Apple's tech note and scan until you find your model in the left column. The power adapter it shipped with and is recommended is in the right column.
Notes on Compatibility
The first thing to note is Apple's comment about the wattage of the power adapters in the event you happen to be mixing and matching.
You can use a compatible higher wattage adapter without issue, but it won't make your computer charge faster or operate differently. Lower wattage adapters will not provide enough power.
The second thing to note is that in 2012, Apple converted from the Magsafe to the Magsafe 2 connector. The new connector is much thinner and wider, so if you have an older Magsafe charger, it won't fit in the latest MacBooks Air/Pro. It's too thick.
Magsafe 2 is much thinner. Image via Jersey City Repair.
Used with permission.
However, you can buy a Magsafe to Magsafe 2 converter for about US$10, and that should take some of the heat off Apple for its periodic changes to the power adapter connectors. For example, if you need to go from a Magsafe 2 power adapter back to an older MacBook Pro/Air with Magsafe, there is no Apple supplied converter, and you'll have to hunt for an older, compatible power adapter on the Internet.
Magsafe to Magsafe 2 converter
Image credit: Apple
Some older models of MacBook Pro/Air shipped with what's called an "L" shaped Magsafe connector. You can also use that with the Magsafe to Magsafe 2 converter described above.
Finally, all this brings up a good point. It's a great idea, after you buy a new Apple notebook, to buy an additional power adapter for travel. Having an extra one protects you against the day the original power adapter fails, and you're scrambling to find a replacement—given that Apple may have moved on with its currently shipping designs.