If you're coming from the US, your CPAP probably uses 110V and the standard US power plug. Check the UL label on your machine to see if it is 110V only or if it is 110-240V (which is becoming more common).

If it's only 110V, you'll need a travel power transformer (a converter is too light-weight and isn't something you should leave running all night), and you'll probably need a plug adapter, in any event.

Check the website of the manufacturer for your CPAP - many models have travel kits that either allow the machine to run on a rechargeable battery or have the necessary adapters.
Cheers,
Bev