I have a powervar abceg251-11 who's PDF is here: http://powervar.com/wp-content/uploads/2016/06/GTS-00074D-Specs.pdf
I am looking for a driver that will work with freenas as shown in the image bellow. Should I try each one and see what works or is there a way to add drivers?
For my part, I've tried the closest UPS description possible for my APC branded UPS, and it worked. I had to fiddle a bit to identify the USB port it was on, but I read the doc, and no problem occurred thereafter.
You can try a few, but if that fails, there is plenty of threads in the FreeNAS forums.