Was in Waitrose yesterday, queueing for the self-service checkouts, when the power went off - lights (most) and all the chiller/freezer cabinets all stopped. Only for a few seconds, but long enough to reboot anything which wasn't on a UPS, so it was interesting to see what was on a UPS.
All the attendant tills and the self-service checkouts carried on without noticing. The self scan checkouts (where you carry a hand scanner around the store with you, and just download it into a dedicated till at the end) all died and people had to wait for them to reboot.
Initially I though that a bit strange, but actually it made sense. The tills where you take time to scan each item through were obviously on a UPS, so staff didn't have to unpack the scanned goods and start again. The self scan checkouts which are a single operation to upload all your goods were not on a UPS, but in this case you still don't need to unpack the shopping, as it's all held in the battery powered hand scanner.
Anyway, interested me that someone designing the system had given it this much thought.