PSU Control and sensing

I use PSU Control to trigger my PSU via the PS_ON pin on my RAMBov1.1b and a relay to my meanwell 24V power supply. M80 and M81 work great.
How can I use M80 S and the sensing options in the plugin?
I don't have an LCD and the RAMBo is powered first before over USB the PSU. Can I use that gcode to check the PSU status? I didn't find an exact fir to my situation in the search.