A bad PSU is not at all comparable to a hard reset. A bad PSU can cause individual writes to fail without the entire computer shutting down, and these failures can and will happen simultaneously across multiple disks since they are all connected to the same faulty PSU. If a filesystem wanted to guard against this kind of failure, I suppose it could theoretically stagger the individual disk write operations for a given RAID stripe so they don't happen simultaneously. (Implementation is left as an exercise to the reader.)
I don't mean to be critical of you, restic, or your backup strategies, but it doesn't seem like you know. ZFS is the I really need to know filesystem. I think it's pretty great and I use it where I can. But if it's not for you, it's not for you.
And FYI, an power supply failure does not manifest the same as a power outage.
As mentioned, it was not usually manifesting as power outage. Random components would fail. Presumably because the PSU was able to keep the system nominally "running" but not delivering the right power to components.
I also experienced some random reboots, things that also looked to me like bad memory... I suspected bad memory at some point. But swapping the PSU did the trick.
How does power fluctuations or cutoff cause data loss in ZFS?
I frequently force shutdown my laptop and PCs with ext4 when they hang, and never lost data.