Here’s something that has happened to my laptop supply a few times:
After having not used it for a few hours (ie home just home from work or on waking up), I’ll find the laptop off and the battery dead. Checking the power supply with a meter, there was no output voltage. The first time it happened, I assumed that the cable between the supply and the barrel connector got pinched or something and I actually cut it off at the supply to check continuity. I was puzzled to find that the continuity was intact on both leads and, checking again, even more surprised that the output voltage had been restored!
I still haven’t figured how it is triggered or why but the supply apparently goes into shutdown and needs to be removed from AC power for a few minutes to reset. Of course, this would have been nice to know BEFORE I’d snipped the cable but nothing some solder and shrink tube couldn’t fix. This has happened maybe three or four times since the first and, while annoying, the fix is easy.
So to the OP, unplug it from the wall and check it again in ten minutes or so.
It may just fire up again, mine did.