Looks like that applies more to laptops than desktops.
What about not specifying the -xml parameter. It should then create a html file, at least it did for me.
Never mind, I see you said you only used the -energy parameter.
I ran it on my desktop and it created a html file as output, not xml.
This is what the built in help says:
Analyze the system for common energy-efficiency and battery life
problems. The ENERGY command should be used when the computer is
idle and with no open programs or documents. The ENERGY command
will generate an HTML report file in the current path. The ENERGY
command supports the following optional parameters:
Usage: POWERCFG -ENERGY [-OUTPUT <FILENAME>] [-XML]
POWERCFG -ENERGY -TRACE [-D <FILEPATH>]
-OUTPUT <FILENAME> - Specify the path and filename to store the
energy report HTML file.
-XML - Format the report file as XML.
-TRACE - Record system behavior and do not perform
analysis. Trace files will be generated in
the current path unless the -D parameter
-D <FILEPATH> - Specify the directory to store trace data.
May only be used with the -TRACE parameter.
-DURATION <SECONDS> - Specify the number of seconds to observe
system behavior. Default is 60 seconds.