Hi, I took it apart. I checked 4 big power mosfets - they all switch, they are ok.
I noticed, that the area near power mosfets gets really hot. I can't even touch some components for longer time, they are really hot.
If I run sourcemeter without power mosfets it outputs still - 16 V, no matter if the output is switched on or off. The output slightly changes when I set some output voltage on the front panel.