From another social media site:
You can ask your cabin steward for an extension cord and distilled water when you board, but it’s better if you pre-order them. That way you’re sure they will be there waiting for you in your cabin when you board. Either way, it’s free of charge.
To pre-order an extension cord and distilled water for a CPAP machine, go to the Princess website then click on “Booked Guests” at the top of the page.
Log into your account using either your login credentials or your booking number.
Once you’re logged in, click on “Access Cruise Personalizer”.
Select “Check-In”, then scroll down to the “Guest Check-in Status” section.
Click on “Dietary Requests”, and tick the box next to “Distilled water (for CPAP machine use ONLY)”.
Then click on the “Send Dietary Restriction” button.
Your distilled water and an approved extension cord will be waiting for you in your cabin when you board. If it’s not there, check with your room steward.
I ALWAYS pack a long (12 ft.) non-surge protected extension cord with my CPAP machine in case they don’t have one available.