Along with all the other bells and whistles covered last week, the new MacBook Pro with Retina display and MacBook Airs also sport MagSafe 2 power connectors. It’s a slight redesign on the current models, so your old spare MagSafe adapter or the ones from an Apple display won’t fit in the new ‘Books.
This isn’t something insurmountable; Apple offers a $10 converter that allows you to connect a MagSafe adapter to a MagSafe 2 equipped MacBook. There’s only one small thing you’ll want to be mindful of.
While the wattage for both adapters is the same 45W, the voltage is different. The new MagSafe 2 adapters output at 20 volts, while the original MagSafe adapters only output at ~18 volts. So if you use that converter to hook an older MagSafe adapter to your MagSafe 2 MacBook, charging can potentially take longer, due to the lower voltage output compared to the newer adapters.
We don’t foresee any catastrophic problems from this, just the minor inconvenience of longer charge times when using the older adapter with the converter. How much of a difference there will be, we can’t say at the moment; we’ll have more info once the adapters are available and we can test it.