The strong smell of many plastic products from China may have many origins. Sometimes it comes from the chemicals used to remove the parts from their injection molds (that is described sometimes as an acetone or butterscotch smell). Washing with water and soap usually gets rid of that type of smell. Another reason for the smell comes from fumigation of the containers carrying the products (that smells like gardening sprays). Washing should again help remove this smell.
Another type of smell comes from the plastics. If the case includes some type of PVC, the smell could be outgassing of phthalate
plasticizers. Washing will not help. It is also commonly used as wire insulation. The more flexible the PVC the more the need to add phthalates. Many phthalates are banned in children's toys in the US. If the stuff is outgassing, it can take years for it to stop.