You need to have subject-verb agreement, so you use differ after a plural noun and differs after a singular noun.
How to interpret this is nuanced, but, simplistically, both of these are correct:
✔ Belgian and Swiss chocolates [plural] differ from American chocolates.
✔ Belgian and Swiss chocolate [singular] differs from American chocolate.
Also simplistically, both of these are incorrect:
✘ Belgian and Swiss chocolates [plural] differs from American chocolates.
✘ Belgian and Swiss chocolate [singular] differ from American chocolate.
However, it's sometime's not as simplistic as that. (I provide another analysis at the end of this answer.)
Understanding this, all that remains is how you parse the noun—if you're actually referring to a plural (countable) entity or a singular (mass) entity. But however you interpret that, the verb needs to match the noun count.
I had a comment suggest that this is wrong because the following is used:
The hot and cold water are provided separately.
But that still matches what I'm saying. In that sentence there are two things (hot water and cold water) and they are provided separately. The most important thing is matching the number of things with the correct verb form.
Whether you decide to put an s on the end of a combined plural noun (the hot and cold water or the hot and cold waters) is simply stylistic; it's immaterial to the form the verb should take.
In some cases, the syntax alone is insufficient to determine singularity or plurality. It depends on how you parse the sentence.
For instance, both of these are possible, depending on context and interpretation:
✔ 1.The choir was singing.
[Commonly US English, where choir is treated as a singular noun.]
✔ 2. The choir were singing.
[Commonly UK English, where the choir is treated as a plural noun.]
✔ 1. My fish and chips was delicious.
[I ate the single food item of fish and chips from the menu.]
✔ 2. My fish and chips were delicious.
[I ordered two food items: an order of salmon and a side of chips.]
In all interpretations of the noun, if you consider the noun to be singular, then it takes a singular verb; if you consider the noun to be plural, then it takes a plural verb.
Revisiting the start of this answer, if you style the spelling of the noun differently, such that Belgian and Swiss chocolate is considered a plural, then the following would be correct:
✔ Belgian and Swiss chocolate [plural] differ from American chocolate.
The spelling of this sentence exactly matches the earlier spelling in which I said the sentence was incorrect. However, it's incorrect when the noun is considered a singular concept, but correct when it's considered a plural concept.