@Hannes_5253 awesome! Thank you for this posting, it's helping me to get a nut client installed. Note for folks coming across this later I needed to use the following to install the nut-client:
yum -y install nut-client --enablerepo=epel
It would be cool if xcp-ng came pre-installed with nut-client and a default configuration that shuts down the xen server & turns off the ups after it finishes shutting down... similar to how truenas has a service which can be enabled to do so. You'd have to configure it of course, with the nut server to monitor, credentials, and some other options such as whether to actually powerdown the ups after shutting down or not, but maybe through a nice gui after turning it on. Seems like everyone should be using this setup ... just a matter of time till they are ready to.
Another reason this would be nice to be integrated, is that docs recommend setting up a user account for nut, one for the monitor so clients can access and another for the shutdown so one of the watchers doesn't change the shutdown script & nut provides a file that indicates when the ups should shutdown, so having that be the same on all xcp-ng systems rather than custom solution would be good.