So it seems I was missing the point of fink a bit.
had to do:
sudo apt-get update
fink install nut
Updating the package lists with apt-get update also fixed finkcommander.
After installing nut (5mins) Setting up the config in /sw/etc/nut/ as found on the net
uncommenting a line:
MONITOR ups@<ip of synology> 1 monuser secret slave
After which sudo upsmon still gave an error of a missing library.
Error:
dyld: Library not loaded /sw/lib/libssl.1.0.0.dylib
For this I installed openssl 1.0.2 using finkcommander
(fink installed a version too high)
Then running sudo upsmon no error was given.
Following https://community.netgear.com/t5/New-to-ReadyNAS/NUT-on-OSX-10-6-Sharing-a-UPS-with-ReadyNAS-and-Computers/td-p/661293
Showing 3 processes (one grep upsmon to be ignored):
ps aux | grep upsmon
And finally showing me the info of the ups:
sudo upsc UPS@<ip of nas>
All that's left is auto starting upsmon on boot by adding the following :
(credit https://superuser.com/questions/1228972/how-to-automatically-launch-nut-client-at-boot-on-macos/1358980#1358980). Edited to add "s" to LaunchDaemons.
sudo nano /Library/LaunchDaemons/org.networkupstools.upsmon.plist
and fill it with:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>org.networkupstools.upsmon</string>
<key>OnDemand</key>
<false/>
<key>ProgramArguments</key>
<array>
<string>/sw/sbin/upsmon</string>
<string>-D</string>
</array>
</dict>
</plist>