You're running with UAC on, so your administrative accounts are running as
standard users most of the time, and you will get the prompt when you need
to do something with administrative powers.

Try piping the result to a file that's somewhere a standard user would have
write permission.  (For example, c:\users\<myuser>\files.txt).
Otherwise, run the cmd prompt as an administrator (right click the shortcut,
"run as administrator").