I use this in combination with homebridge and homebridge script plugins. 
These are plugins that allow you to execute scripts to turn on/off and check state of different devices via homekit/siri
I use this one https://github.com/luisiam/homebridge-cmdswitch2.
I've written the on.py, off.py, and state.py scripts to be able to use the RPC3 outlets with homekit and the home app.
There were some challenges with number of telnet sessions that the RPC3 unit allows at a time. 
I've tried to minimize having to telnet into the RPC3 unit by using a status file to keep track of outlet status.
The .sh versions of the scripts simply call the py versions. I configure the homebridge plugin to execute the sh scripts.
You should pass the sh scripts the outlet number as the first parameter and the user name as the second parameter.
Though right now the py versions of the on,off and state scripts all hardcode the username to "None".  
My RPC 3 unit is set to not ask for username or password.

More info on the Baytech RPC3 
http://www.copyerror.com/2014/04/25/baytech-rpc3-remote-power-controller/
https://www.servethehome.com/baytech-rpc3-deal-remote-switched-8port-pdu-50-windows-app/

This script requires pexpect
https://github.com/pexpect/pexpect
Install using pip:
pip install pexpect