yep GET A NEW PSU serously chances are it will bet at most another 30-40$ unless your runing multiple gpus get a quality unit in the 500w range from one of hte following, corsair, seasonic, xfx, antec, evga
Why is it too late? That PSU is indeed bad. If it's possible, ask them to change it (They build PCs in their store so this PSU will be used in another build anyways).