The power on Emerald Star ships is 240Volt, European standard plug. There is a single 110 Volt North American type outlet in the bathroom.
Since I was spending a week in London prior to my Emerald Dawn cruise, I bought a universal adapter that includes 4 USB and 1 USB C charging ports: It's $24 at Amazon
https://www.amazon.com/gp/product/B0B8SLNBDP/