mrsduck - I have been on 9 cruises. On 7 of them I have brought a power strip and never had difficulty plugging a three pronged plug into the outlet at the desk in the cabin.
Carey - I have never had that problem, but I usually have only two (max three) things plugged into my power strip. You will find that the power to your strip fluctuates (never goes off but it is not a steady stream of power.......I found that out when a friend plugged in an alarm clock (not battery operated) and it constantly fell behind real time.