When there is no budget for a rackmount NAS, then only one PSU is to be found on the back of a desktop model. What is the advantage of having two PSU's in parallel ? What is the difference ? In emergency situation, power drops anyway, so one needs to count on the UPS in both situations, not ?
Yes, having a dual PSU protects you from the power supply failure. This happens statistically often enough to consider it as a threat. It might take few days to get a replacement part.
So far NAS have several redundancy options:
-Multiple HDDs
-dual UPS
-dual motherboard/ controller board
-also dual NAS (high-availability option)
all this ensures uninterrupted service.
I hope this helps.