I doubt the MOSFET is stopping the supply starting.
I think you will have to find the part number of the regulator and look at a data sheet to see its startup characteristics.
Just as an example, your mains is 90v to 240V and the regulator needs perhaps 15V to operate. Where does it get it? Sometimes, it gets the 15V from a winding on the transformer, but then you need another source of power to start. So you could have a large resistor and series diode going to the mains to charge the regulator supply cap initially, and have the regulator draw no supply current until a startup threshold is reached. Once the regulator starts, it will it will get all ongoing power from the transformer winding. So you could have a thermal problem in this startup cicuit - a dry joint, a leaky capacitor, a faulty resistor, etc.
The other thing is it is trying to start, but the start fails, and the regulator has a startup timer, so it waits a second or so before another startup attempt. If the supply has a ON LED, you might see it blinking in this case. The supply need to deliver extra power at startup, and for some reason that ability to get the voltage up at the start has been affected. It could be something like the capacitors across the rectified mains are deteriorating, or it could even be something in the Airport that adds extra load when the Airport is warm.
Richard