Not quiet an encyclopedia, but as a child I really liked The Top 10 of Everything books.

This was late the late 90s, we had dial-up, but internet was still in its infancy.

I definitely had the 1999 and 1998 editions:

Microsoft Encarta was also mind-blowing for its time, especially if your were a child in the late 90s and early 2000s.

I remember reading this as a child in the 90s (I was living in South Asia at that point).

Strange to think about it now.