Hello friend, how are you? First of all, I think the problem with ur resolution or graphics isn't due to power supply. I think the problem is with your VGA Card or VGA Drivers. So try to uninstall the drivers for your VGA and reinstall them or simply upgrade the drivers.
If this solve your problem then okay otherwise reinstall ur windows.
Secondly conecting powersuplly of more power then specified for ur system will cause serious damage to ur system. So do not connect any power supply without authentic information.
Also try to change the resolution or this problem also because of your monitor. So make sure that ur monitor is working properly.
I hope this will solve your problem. Take care of you and others and be happy.
Bye...
Dur-E-Wahab