DPMS does not standby my Samsung monitor

I own a pretty old Samsung BX2250 monitor, which I would like to be able to set to standby using dpms, like

xset dpms force off

The expected result is the monitor going to standby. The actual result is, that the monitor turns black, then it says "Check Signal Cable". I also messed around with

xset s off

as I read somewhere this interferes with dpms, with the result that the screen turns back on immediately. Using standby and suspend does not help either. I own a GeForce GTX 960 graphics card, using the nvidia-440xx driver on a Manjaro, which uses x11 (by trying this: https://unix.stackexchange.com/questions/202891/how-to-know-whether-wayland-or-x11-is-being-used) . I remember back some days with my old PC, it went to standby mode. Unfortunately, I cannot remember what I did to achieve that. Does anyone have suggestions?