Brown-out protection?

[K4680]

Understood, and that's what I assumed was happening in my original post.  What I am not clear about is how it distinguishes between me pulling the mains plug out and then putting it back in a few seconds later, in which case it powers up normally as I described earlier, and the situation a couple of nights ago where the mains power obviously failed and then came back again, in which case it stayed stubbornly powered down.  I suppose there must be some logic to differentiate between total power loss and under-voltage or varying (RMS) voltage, for-example.

Hi, that's exactly how it is. Limits for voltage, frequency, etc. are stored. Every time you switch on, the limit values ​​are checked, everything is ok.