Thank you for this fast answer... Indeed, the PS recovered after about 30 hours of pause, I think get a spare one to avoid further "waiting time"...
The heatbed still does not manage to raise temperature (sensor reports the ambient temperature around 20°C), but the servos are working (X, Y, Z and extruder). I've read some things about the connector which doesn't seems to be very reliable...
I had a power supply that I gave up on and then a week later it works fine. I bought a 3rd power supply and all 3 work but sometimes they need to rest a few days. Once they come on and the printer starts printing I've never had a problem. It's only when the printer is off. This is probably unrelated to your problem.
I also hear the very quiet "hissing" sometimes.
I doubt there is any kind of serious short on your machine. I think it would be a more consistent problem.
Contact support now because it may take a few weeks to get a new power supply if you are still in warranty. If you are no longer in warranty these power supplies are easy to find. But expensive.
I also once had problems with K1 relay where my bed was cold and servos wouldn't move but everything else worked fine. Here is a video talking a little bit about the problem and a solution. The final solution (with advice from a founder of UM) was to jumper K1 out as it isn't really used:
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