Where is the main power supply fuse on - 1999 Ford Expedition

There is no separate fuse for power windows:
https://www.2carpros.com/questions/nissan-altima-2006-nissan-altima-windows-and-locks

https://oards.com/causes-of-power-windows-not-working/

Power is supplied at all times: ? from 30A fusible link (Letter , located in the fuse and fusible link box) ? to circuit breaker terminal s1 ? through circuit breaker terminal s2 ? to power window relay terminal s5 . With ignition switch in ON or START position, power is supplied: ? through 7.5A fuse [No. located in the fuse block (J/B)] ? to power window relay terminal s2 . Ground is supplied to power window relay terminal s1 : ? through body groundssM68 andsM14 . The power window relay is energized and power is supplied: ? through power window relay terminal s3 ? to main power window and door lock/unlock switch terminal s1 , ? to power window switch RH terminal s4 .

https://www.nicoclub.com/FSM/Frontier/2000.0_Frontier-VG/el.pdf

Is it a stand alone unit or a mains powered unit?
If it is stand alone you might have to disconnect any battery fitted and remove the switch. Remove the wires from the back of the switch.
If it is mains powered either unplug it at the wall or remove the fuse at the main fuse panel. Replace the switch and reconnect the electric supply.

There would be something like a main fuse link, or on newer trucks some large fuses under the hood- one or two would supply power to the ignition switch. But a main fuse link would pretty much supply power to everything. If it went out, you would have no electrical power anywhere. Before the use of large maxi fuses, many vehicles had numerous fusible links, one for lights, one for ignition switch, one for AC or cooling fans, and so on.

Follow all the wires or cables from the positive battery post. A main fuse link would be on a pigtail from the main cable.

Main relay ? where are you missing power ? In the under hood fuse / relay box check IGN 1 an IGN 2 fuses both 50 amp .they supply power to most of the vehicle !

PGM-FI main relay 1 (FI MAIN) is energized whenever the ignition switch is ON (II) to supply battery voltage to the ECM/PCM, power to the injectors, and power for PGM-FI main relay 2 (FUEL PUMP). PGM-FI main relay 2 (FUEL PUMP) is energized to supply power to the fuel pump for 2 seconds when the ignition switch is turned ON (II), and when the engine is cranking or running.

For sure the main supply is cut, check the line back to the main relay board inside the engine room. check for a main fuse or a link failure.
You have to trace this break and that can be the fault.

the main relay, located at the back of the fuse box, is a coupler type which contains relays for the ECU power supply and fuel pump power supply.

this model dont have fuel pump fuse , the ecm supply power to pump, check EFI fuse 15amp , if good, then remove rear passenger seat, to check the fuel pump , give me for notice please

i would suggest that u start to check power from 85A main fuse it supplies the power to all those circuits! circuit must be open!