My Sony Vaio laptop switched off and wouldn't come on.I am sure the fault is from d Power Supply unit.Pls hel?

I meet someone who could repair it and he explained that a circuit board that accepts AC voltage from the power pack and rectifies it before distributing it to the motherboard components had gone bad and needed to be changed.I am finding it had locating the exact component cause I don't know the exact name of the component.Pls I need help and advice on this.