Civil Services Examination is such where you have to take a call. If you have interest and wants to go ahead with Public Administration as optional subject, you should take a rational decision.
First, be clear that post-graduation in Public Administration does not ensure you desired success so instead of masters, you should seek proper guidance and for that you may join a good coaching institute that imparts Civil Services Examination oriented coaching.
Public Administration is one of the most popular optional subjects and has helped many achieve success. It is a dynamic subject and has some specific requirements to meet. If you are able to understand the examiner’s intent, you will be able to perform well.
You have many good coaching institutes in Delhi offering guidance for Public Administration. Synergy (M K Mohanty), Pawan Kumar IAS and even Vaji Ram & Ravi also offers courses for Public Administration that will give you confidence to go ahead.