I've never seen a redundant PSU be worse than a single PSU, actually (like the dual-line-cord modules on many servers or network devices). PSU failures have gone way down in the past 15 years or so that I've been observing them. The only power supplies I routinely see dying are external transformers on low end network devices and on systems exposed to really dirty power.
I have seen facility-scale UPSes go bad, and sometimes in weird ways, but an order of magnitude less frequently than grid power.
I think we reached a crossover point where designing for facility-scale survivability vs. replicating facilities ceased to be worthwhile for most Internet applications sometime in the past 10 years. It doesn't really make sense to drop $2b on a ~100k sf datacenter like AboveNet used to do for e.g. 365 Main. There are still some systems where replication is a pain, but even for those, I think metro area replication shouldn't be that hard. Even just running 5km of fiber in a loop between a few buildings in the same town gets you a huge amount of resilience against most facility problems.
I have seen facility-scale UPSes go bad, and sometimes in weird ways, but an order of magnitude less frequently than grid power.
I think we reached a crossover point where designing for facility-scale survivability vs. replicating facilities ceased to be worthwhile for most Internet applications sometime in the past 10 years. It doesn't really make sense to drop $2b on a ~100k sf datacenter like AboveNet used to do for e.g. 365 Main. There are still some systems where replication is a pain, but even for those, I think metro area replication shouldn't be that hard. Even just running 5km of fiber in a loop between a few buildings in the same town gets you a huge amount of resilience against most facility problems.