Take it apart and see if any of the caps are bulging or ruptured if they have toss it I would not recommend trying to repair it a faulty power supply could burn out every component in your case so it really isnt worth risking your whole system. If all the caps are fine and it seems to be functioning correct you can replace the fan but anything more then replacing the fan I would say trash it.
You can fix faulty power supplies and I do on a regular basis. However I am an electronic engineer with many years experience and have all of the necessary test equipment, and even then I find that computer power supplies are very difficult to repair. I obtain parts which are difficult to buy from other faulty power supplies which have faults that I can’t fix. Computer power supplies can have catastrophic failure where many parts are destroyed and more importantly the PCB is carbonized rendering it unrepairable, the fact that you can smell burning makes me think that your power supply is not repairable as you cannot in general smell a blown capacitor.
I agree with the other veterans. If it is just the fan, then it can be replaced. If it is anything more comlicated, then toss it. Is the psu still under warranty? If so, then maybe you can get a free replacement. Well.....almost free. You'd have to pay to ship the faulty unit.