Major differences between state Public Service Commissions (PSCs) and UPSC include the scope of exams, selection criteria, and the administrative services offered. UPSC conducts a more comprehensive examination, covering a broader range of services across the country, while state PSCs primarily focus on state-specific services. Additionally, UPSC has a standardized nation-wide pattern, while the format of state PSCs can vary. The levels of competition and the syllabus may also differ, impacting preparation approaches and required skills for aspirants.