Given devuan-alpha, installed both xfce4-dektop and mate-desktop:

Login mate-session, 2 Issues:

• xfce4-power-manager gets launched, mate starts it's own
• System Menu / Settings : shows 2 entries for "power-saving" settings

The bugs are in the .desktop -files:

• xfce4-power-manager/settings/xfce4-power-manager-settings.desktop.in
• xfce4-power-manager/src/xfce4-power-manager.desktop.in

FIX:

- NotShowIn=GNOME;KDE;Unity;
+ OnlyShowIn=XFCE;