Sherry is made from a blend of old (oxidized) white wine from several years that is then blended and fermented. While it may contane a slight "hint" of vanilla or "floral citrus" - it doesn't taste anything like either vanilla or orange/pineapple juice in the substitution that texasgirl found for you. (and I'm not picking on texasgirl in any way ... she was kind enough to go out and look for a substitution for you ....) HanArt had a good idea, while white wine would be "closer" - it's not going to have the depth of flavor or character of Sherry - do DO stay away from anything labeled "Cooking Sherry" - it's crappy stuff that is undrinkable to begin with and has had so much salt added to it that it's even more undrinkable.
This is kind of a classic way to finish off some soups. You would be better off skipping it than to mess up your soup with substitutions.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain