I have read many books and articles about Service Design. However, I can't figure out the following question:

What's the difference between Product Design and Service Design?

For example, let's adopt your definition and use "product" to replace "service":

[Product Design is a non-aesthetic design practice that helps product providers offer a benefit to users. The user-centric tools and techniques of the practice allow providers to achieve more predictable, successful outcomes. The tools and techniques used by product designers are used to design new products and address concerns or challenges with existing products, such as whether to improve the product, alter key parts of the product to adopt to changing circumstances and assess the value of a product to users and providers alike.

Furthermore, a successful product is one that 'satisfies' the needs of users by having them achieve a desired outcome through a reliable product experience.]

It works perfectly too!