The command response showing the help section implies it failed.
The password term of config getprop command comes from nethserver’s e-smith database and starts with an uppercase letter.
I’m no expert on nut, but as the password for upsmon user is present on upsd.users file I will suggest to add it to the e-smith (nethserver) database.
First check it is not already set:
config getprop nut-server Password
If empty, you can set it with the value from upsd.users file (replace xxxxxxxxx with the proper password):
config setprop nut-server Password xxxxxxxxx
You can check available UPS settings with:
upsrw -u `config getprop nut-server User` -p `config getprop nut-server Password` `config getprop nut-server Ups`
or directly with the known values (xxxxxxxxx represent the password):
upsrw -u upsmon -p xxxxxxxxx UPS
Same goes for chaning settings, were the paremeter
-s is added.