amd 7750 is the best card which require low psu i.e 400w (although in flipkart it is 450 w)
Its price is continously increasing in flipkart (from 6660 to 7247)
Check yourself its performance
7750,PassMark - Radeon HD 7750 - Price performance comparison
you can also go for gigabyte 7750 for rs 6660,GIGABYTE GV-R775OC-1GI GRAPHIC CARD
it is economical,require less power supply,and also can run all games in middle - high graphics