I would agree with the controller chip being a candidate. I've repaired a number of power supplies in my time and it was about a 50-50 chance that when the main FET blew as to whether the controller IC blew. And then it could be either that the controller IC shorted the gate pin to ground or to Vcc, if it was Vcc then bye-bye fuse. If the power supply was subject to a surge it's possible the controller IC was damaged and the FET looks OK.
Also don't rule out the possibility of the FET having suffered some less-than-obvious failure. If you test the resistance with just <1VDC from a multimeter it wouldn't reveal any leakage current that appears under high bias voltages.
I had an LG 50PS3000 plasma TV that had a bizarre failure like this. A 100V rail on the Z-sustain board, used to bias the plasma panel for some part of the display cycle, was generated by linear-regulating the 200V sustain supply down. It had a moderately sized heatsink on it and average current measured around 50mA in operation. So probably dissipating around 5W. As the FET increased in temperature the Vzbias voltage would increase progressively until it hit 150V, at this point the plasma discharge was very bright and the main PSU would shut the TV down (the picture essentially just became brighter and more distorted, at one point the PSU sounded very angry and ~1000W was pulled from the wall! Normally it is about 400W.)
The cause was that the FET was bad, I guess years of being at a sustained temperature had somehow caused a slow leakage to build up. But take the FET out of circuit, drain-source measured >1Meg. Heat it up with a heat gun and it dropped to ~100k, but still didn't seem obviously bad. It seemed whatever effect there was, it depended on the voltage across the device.
A little trick: if you have access to a current-limited 80V+ PSU, many small flyback based universal-voltage AC PSUs will start up at quite a low voltage. You can then try to see what is going on with a scope without fearing (too much) about getting a shock or weird grounding etc.
Since the PSU only produces 12V and 5V, maybe it is easier to find a replacement PSU, or add an external PSU like used by external drive bays that outputs 12V/5V.