Hi Jammowem.
From Marellas online site.
19) Can I take electrical items onboard a Marella Cruise ship?
In your cabin personal grooming items such as hairdryers, travel irons, curling tongs, hair straighteners and shavers are permitted when used with proper caution. However, if such devices are determined to pose a hazard, they will be removed and returned on the last day of the cruise prior to disembarkation. We also ask that all electrical equipment is turned off when you leave the cabin and not left on charge.
You may bring a four-way adapter or extension lead onboard, but we ask that you let our Cruise Team know so that these can be tested.
22) Can I take a travel iron on a Marella Cruise ship?
You may take a travel iron on the ship, however if the device is determined to pose a hazard they will be removed and returned on the last day of the cruise prior to disembarkation. There's also a laundry service onboard the ships where you can pay for your clothes to be pressed on-demand. If you've chosen a cabin with premier service, you get a free pressing service for the formal night.
I would imagine that a steamer would come under section 22.)
as an aside we have never been asked to get any adapters tested.
Hope this helps.😉