Get a bigger Power supply. It is hasn't exploded already It will during Overclocking. That GTX is power hungry and your CPU will consume more power if you OC it.
He doesn't need a new PSU. I know the whole deal about amps vs watts, but the PSU has 38A combined on the 12v rails. The GTX doesn't use more than 150W, and a e6400 even OC'ed won't draw more than 100W.