Not really. But the rule is not without exceptions! E.g. Foodstuffs. Butt in this case, "stuffs" has another meaning. Stuff is uncountable. Countable "stuff" is a thing. Compare: 1. Water is useful stuff. 2. Phones are useful things. Every countable noun in English can be replaced by "thing" or "things". Every uncountable noun in English can be replace by "stuff". If I am correct, Chinese has only one word: 東西. Is that right?

No, it is uncountable.