When the user disables (unchecks) the option "Monitor power management control" I think that the proper (and user expected) action should be not to change in any way the previously or future active DPMS settings. For example, if I have used xset from .xsession, the power manager should not overwrite my current settings. However, xfce power manager does RESETS the standby/suspend/off to 0 and disables DPMS. I have detected this behaviour trying to investigating and solving the conflict with xscreensaver. Up to date I had no luck with both xfce4 power manager and xscreensaver installed at the same time. DPMS management only works when I uninstall one of them, no matter if the other has "DPMS disabled" or not. Screensavers are useful for LCDs prone to burning (I want a black screen, but not a frequent set of power off/on cycles). I have ended enabling the standard xorg screensaver (xset s on s noblank s 300 10).
I must confess that the "Monitor power management control" has in fact a tooltip (I didn't read it) clarifying his action: "Disable DPMS e.g don't attempt to switch off the display or put it in sleep mode" To honor this tooltip, I agree that Power Manager must disable DPMS; otherwise the X defaults could power off the screen contrary to user desire. Anyway, it should perhaps be available a third option: 1) Disable DPMS 2) Control DPMS 3) Use X defaults Power Manager is useful for several different tasks, but currently you are obliged to leave it control DPMS among them (it does indeed a fine job there, but may conflict with other tools trying the same).
This option is utterly confusing. First, it is not clear whether "monitor" is a verb or a noun. (The words "screen", "monitor" and "display" are all used in xfce4-power-manager-settings, maybe sticking to one would be better?) Second, does the negative form in the tooltip refer to when the box is checked? I.e. check the box to disable DPMS?
*** Bug 10192 has been marked as a duplicate of this bug. ***
From functionality point of view, when the function is disabled, the dmps settings should clearly be untouched. Please see the duplicate I have reported for further details.
This is indeed the case now. 1) The naming has been improved so the option should be clearer (incl the tooltip) 2) The DPMS timeouts are not reset to 0, instead they are left as set up (e.g. by xset)