|Sorry, I had to walk away...|
A 'decent' power supply for entry level gaming would be like this one:
It has a single 12Volt rail, 80% efficiency rating (bronze level certified), active PFC, 32Amps available on the 12 Volt Rail, 3year manufacture's warranty, and a quality name brand.
Note: +3.3V@20A, +5V@20A, +12V@32A, -12V@0.8A, +5VSB@3.0A the 3.3V & 5V rails are not overinflated as they are on many cheap power supplies and the more useful 12Volt rail has honest-to-goodness Amperage to power your graphics card, probably more than many cheaper "500Watt" and "600Watt" models you will find sold in India.
To sum it up, you will need to purchase a quality power supply first before you look for a graphics card, even if this means that you need to put off purchasing the graphics card a few months to get what you actually need, rather than wasting money on a card that will not meet your needs. If you need to confirm exact compatibility of anything, you need to list the exact components by make and model number and/or the make and model number of the computer system you own and if it is not a name brand (HP, Dell, etc), include a link to the model on the internet.
You have to be a little bit crazy to keep you from going insane.