ArchWiki - Xfce - Display Blanking
Xfce Power Manager
Xfce Power Manager controls DPMS settings only. They can be configured in the Power Manager GUI within the Display tab.
Note that when Display power management is turned off, DPMS is fully disabled, but this does not mean that Power Manager will simply stop controlling DPMS. However, it does not control screen blanking, which may remain enabled even after display power management is disabled.
To disable both blanking and DPMS, right click on the power manager system tray icon or left click on the panel applet and make sure that the option labelled Presentation mode is ticked.
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