Make your Windows system accessible over Ssh.
If the emergency clean shutdown software of the UPS runs on a Linux server, there has to be a way to enter the Windows server from that Linux server to initiate a shutdown.
Windows has always had the dos box for CLI maintenance. The problem was that this had a far from complete command set to do full maintenance from the command line. So Windows introduced a new dos box called PowerShell. Theoretically one could fully maintain a server from PowerShell, to such an extent that you do not even have to install the GUI.
This is all nice and well, going in the direction of what Linux has always had (installation without GUI). But Windows would not be Windows if they did not use proprietary protocols to access the shell, making cross platform access hard and unattractive. There is no Ssh server to be found in your Windows installation, only the very insecure Telnet server which should never be used.
A third party has developed a Ssh server for Windows. It is easy to install and configure, and allows access to the PowerShell of your Windows system from Linux systems over Ssh.
It is payware, but it may be well worth the money in environments where Linux is the leading server OS. The developers are kind enough to also provide a free version. The handicap of the free version is that only one session at a time is allowed.
First download the program at http://powershellserver.com
Then install it and run it to configure it.
On the first tab there is a check box "Run as a service". Check that box. Then push the run button to start the service. Now you're done and can leave the configuration program.
At some point it will ask to save the configuration. Do that. On the save dialog there will be a check box to ask permission for making a hole in your firewall. Be sure it is checked, else port 22 will not be accessible from outside the Windows machine.
Now you are ready to connect over Ssh with a user of the Windows system.