@pushkaraj
its better to have a gud PSU with min 450w, as in future aybe the stock 400w or 450w cannpt handle if he adds some HDD,ODD,more mem, or some USB powered devices like SE phones, portable HDD etc.
And most of all the power consumtion of system increases as it gets older due to components like capacitors nd resistors inside mobo. So it is safe to have a gud powersupply.
Also normal ones cannot stand overclocking, either mem, CPu GPU etc nd may render the system unstable.
Moreover a gud PSU like Zeb Platinum 500 or better with 120mm fan cus also help in overall cooling of the system.