It's all to do with the "Power Rails" from the PSU. If you look at the label on a PSU you will see various Voltage "Rails" or values. The PSU may be fried by the power surge but still providing power through some "Rails".
Obviously in your case not all of them. Get the PSU tested by a local Repair shop. They might simply be able to test it by plugging in a seperate PSU alongside yours and making the connections.
Hope that helps