JaSoN_cRuZe :
Sorry there is no room for PSU upgrade since a quality PSU in India is costly about 5 to 6K INR
I cannot get the RX 470 as you said since it is overpriced and also not available whereas the 570 is cheaper and available(stupid market) currently, I'm just waiting for RX 580 4GB with single 8pin*(Base model not high end).
Are you sure that my psu will provide more than 75 watts from the 6pin pcie (it has 3 yellow wires) so i can use a single 6pin to 8pin to power the RX 570 or RX 580 (or) the 2xmolex to 6pin then 8pin would do it better.
UPDATE: I think my PSU can handle or if not i can undervolt until i get a quality PSU
What's the rest of your build (especially CPU). It's not overclocked is it?
No - I'm not at all sure that your PSU will be fine with an RX580 and hopefully my first post made that clear. Technically with an efficient CPU it **should** be OK, and your PSU is at least decent quality which helps, but you are pushing things further than most people would be comfortable and that does raise your risk. If you're running a hungry CPU like an FX 8370 or something, I'd suggest that risk is fairly high indeed.
Just a month ago a mate of mine blew his old PSU (650W) with an OC'd CPU and hungry GPU, it took out his motherboard and he had to do a full upgrade that cost him hundreds of dollars. He was unlucky, hopefully you're not, but the risk is there.
However, if you choose to go ahead, then I am very confident that you are better with a 6 Pin to 8 Pin than messing with molex or SATA to 8 pin adapters. The 6 Pin will be on a different rail to your CPU power, and as I said previously, those 6 pin connectors have headroom and are designed for high current. Taking this risk involves going out of spec, but you're betting doing that on a 6 pin than anywhere else.