I still wouldn't expect the Americans to come out on top but the distinction might be less than you think. I remember in school that word problems tended to be written very stereotypically for any given book or curriculum, and students who just barely managed to learn how to do that stereotypical set might have a lot of trouble doing problems from a different "word problem tradition" (if I may coin the phrase). You might find more Singapore students have trouble doing the American problems than you expect, even though as I said I'd still expect the Singapore students to come out on top in general.
I don't have current access to students from Singapore, but later this summer I'll have a visit from a student from Taiwan, and I could try American problem types on him.
My two older children have lived in both Taiwan and the United States, as my wife and I have at various stages of life.
I still wouldn't expect the Americans to come out on top but the distinction might be less than you think. I remember in school that word problems tended to be written very stereotypically for any given book or curriculum, and students who just barely managed to learn how to do that stereotypical set might have a lot of trouble doing problems from a different "word problem tradition" (if I may coin the phrase). You might find more Singapore students have trouble doing the American problems than you expect, even though as I said I'd still expect the Singapore students to come out on top in general.