Hello Nisheeth

If are getting a rank of below 500 then you are having a 100 % chance of getting shorlisted for any Psu's. The selection will depend upon how you perform your interview conducted by hem.

As you have mentioned that you can get a rank between 246-269. Awesome , in one word, There are somewhat 7 Maharatna :

1. Coal India Limited( Conducts it's own paper)

2. Indian Oil Corporation

3. NTPC Limited

4. Steel Authority of India limited( Conduts it's own paper)

5. Bharat Heavy Electricals Limited

6. GAIL (India) Limited

7. Oil and Natural Gas Corporation