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If it's for a normal MacBook or 13" MacBook Pro, you'll want a 60W MagSafe. If it's 15 or 17" you'll want 85W. The 85W will also work with the smaller models, but the 60W doesn't work as well with the bigger ones.
 
The 85W will also work with the smaller models, but the 60W doesn't work as well with the bigger ones.

Meaning it will charge the bigger MBPs, but slower, and that during CPU and GPU intensive tasks, the battery could be used along the charger, as the charger does not deliver enough watt.
 
Yeah your link has an extra http in it. But exactly what everyone else said.

13" 60 or 85
15" 85 only
 
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