dress code?

We are going on a cruise on the Sun Princess in May. I have read many things about dressing for the dining rooms. It says jeans are not allowed in the dining rooms. We have several friends that have taken the Sun Princess and they told us many men showed up on "smart casual" nights wearing Levi's or jeans in the dining rooms. One gentleman even showed up on a "formal night" wearing red suspenders. So I am not sure what is expected. And I have a husband who's idea of dressing up is a new pair of Levi's. Any help would be appreciated. Thank you. JudyP