Hi @Alessandro.B, you can try wake-on-LAN on Xavier like here: Sleep state - #8 by Honey_Patouceul
I believe it requires the unit to be in suspend sleep state though, not completely powered off.
If you want to remotely trigger the power supply itself, it may be easiest to use a device like one of these: 5Gstore EZ-22b Single Outlet Remote Power IP Switch - App Controlled, 94 Reviews
You can place a jumper on the Xavier’s Auto Power-On pin, so it automatically boots when power is applied. This may be preferable to soldering/modifying your Xavier, which would void the warranty.
You can also find less expensive power relay boxes that use a physical remote control, or voice command to an Alexa/ect, if you do not require remote networking access to control the power. Or you could wire up your own AC relay to a controller board.