This is from experience;
Due to a power cut there is an almost a certain chance the psu has bee damaged and normally non-repairable,as this has possibly gone it may have damaged your motherboard also.
As said,i have experienced this myself,and both needed replacing.
You could start with a new psu first,easy enough to change over,just check the physical dimensions.
Basically if a full ATX case...buy an ATX psu and so on.