Downgrade your graphics to HD 6670...or save up and wait for HD 7750....either way, you should get a better power supply. The last thing you want to do is to toast your components by using an inferior power supply.
No, that psu will not work it is way to small to power a 7750. You are going to need atleast a decent quality 450w psu or a high end 400w. A good psu for this is going to be ~$50.
No, he won't need 450 watt or 400 watt one. A 250 watt power supply with at least 13 amps on 12V rail would do. However, there's no way a 9 amp one would. I'm sorry.
Either HD 6670 or HD 7750 would work under the 300 watt Seasonic. A 450 watt Antec VP-450 is better for upgrading. But if you are tight for budget....the 300 watt Seasonic would much better than your Chinese no name power supply.
None. 9 Amps on the 12V rail means 108 watts on it. Your CPU may use up to 70 watts. Rest 38 watts are needed by your motherboard. There's nothing left for graphics card.
What is the most powerful video card will in my power supply
No graphics card that can play with the latest games. HD 6670 is pretty well the entry level graphics card for light gaming. GTS 450 would work as well, but that card needs more juice.
No graphics card that can play with the latest games. HD 6670 is pretty well the entry level graphics card for light gaming. GTS 450 would work as well, but that card needs more juice.