I have a valid XF86Config-4 file with DPMS enabled, and I can turn the
monitor off when I run a window manager different from KDE.
However with KDE 3.3.1 I have set DPMS in the display settings of the
control center but it has no effect. The value I entered are here, but
the screen will never shut down.
$ xset q
[...]
DPMS (Energy Star):
Standby: 300 Suspend: 600 Off: 900
DPMS is Enabled
Monitor is On
[...]
Under KDE the command "xset dpms force off" (off or whatever) will do
nothing. My monitor just sits there, as if I had never done anything.