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the 13" comes with a 65 watt adapter, while the 15" (and 17") come with an 85w

it will be fine, but charging will be slower than normal. It will charge faster if the computer is not running (or if it's sleeping).
it's possible the battery may not charge at all, or possibly be discharging while using it, although much slower than if you were completely unplugged.

if it is discharging, make sure to keep an eye on your battery life, as when it runs out, your computer will shut down.

most power adapters these days are good anywhere, you just need something to make the plug fit into the socket. or for most of apple's power supplies, you can swap out the plugs on them.

To be safe you want to check whatever you are plugging in. if it says "100-240v 50-60Hz" you're fine to plug it in anywhere in the world. anything else and you need to check that the requirements match the country you're in.
 
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