Hello.
The very first difference in both the examination is that UPSC conduct National level exam and APPSC conduct state level exam (Andhra Pradesh state) exactly the difficulty level of national level exam is going to be more high in comparison of state level, basically UPSC focus on national  history, National economic, and all subject with national target, while APPSC gives major focus on Andhra Pradesh history, Andhra Pradesh economic, etc that means there is a big difference in the syllabus.
Best of luck.