I think everything has settled on /usr/share/metainfo by now. xfce4-power-manager.git#master:data/appdata/Makefile.am still uses "appdatadir = $(datadir)/appdata" which should be replaced with "$(datadir)/metainfo". see bug#15341
Andre Miranda referenced this bugreport in commit e40a57696e9bd6dedd283f5c2f79c480493ef49a Install Appdata in metainfo (Bug #15380) https://git.xfce.org/xfce/xfce4-power-manager/commit?id=e40a57696e9bd6dedd283f5c2f79c480493ef49a