UPS/surge protector
I'm curious if anyone uses a surge protector or battery backup for larger cracking servers. Our system has four 980s and it's fine when not cracking, but as soon as we spin up the GPUs it pulls too much power & the UPS can't keep up. I'm assuming that's a common thing & it would take a huge UPS to support it the power draw, but I don't know if maybe it's just our old UPS. Is a dedicated surge protector without the battery backup the way to go or do we just need to upgrade the UPS? Any recommendations?
Something like this should work:
IANAE (I Am Not An Electrician), and this is not electrical advice ... but this depends entirely on your own use cases.

If you're OK with cracking being interrupted for significant periods of time, or if you could get an alert when power is lost to the unit, then surge protection would probably be sufficient.

But if you want to rely on the jobs finishing without interruption, get a bigger UPS.
You dont need to be an electrician to realize that any off the shelf UPS isnt going to hold a gpu box cranking at full speed for any meaningful length of time.
I typically do not recommend using UPS for cracking rigs. For one, as radix identified, UPS won't do a whole lot for a cracking rig under load. Most likely won't even keep it on long enough to gracefully shut down, unless you have a serious fucking UPS. Two, password cracking ops likely aren't mission critical and a little bit of downtime is usually acceptable. I don't know of anyone who has a 5-9s requirement for password cracking ops. Three, there is sufficient fault tolerance built into Hashcat (and for my clients, Hashstack as well) that you can easily resume operations when power is restored. So yeah, I wouldn't worry too much about UPS. Direct power is best for most all use cases.