Using DPMS - Energy Star power saving - has changed slightly under XFree 4 compared to XFree 3.3.6.

The full specs for the XF86Config file are at the XFree86.org site, but all you’ll need to do is described below.

Add the following line to the "Monitor" section in XF86Config (use XF86Config-4 if it exists):

Option "DPMS"

That will, after the X server is restarted, allow you to use xset to shut the monitor off.

The monitor will also automagically blank after 10 minutes, and turn off after 40 minutes. (Default values - see the XFree specs for more info).

If you want to modify the times for the monitor blanking, going to standby et cetera and turning off add the following lines to XF86Config-4:

Section "ServerFlags"
  Option          "BlankTime" "0"
  Option          "StandbyTime" "5"
  Option          "SuspendTime" "0"
  Option          "OffTime" "20"
EndSection

The numbers are the number of minutes before each mode kicks in. 0 disables a particular mode.

If you already have a ServerFlags section, just add the Option lines to that.