This may be a niche market, but I'd love to have a PSU that (like a UPS) had a USB connection allowing the PC to monitor the current power state of the PSU.
This might help find situations where input voltage is sagging and (like a UPS software alarm) you want to shut down. More advanced features might even be a list of the currents drawn from each rail, so you can see when your graphics card is maxing out one rail or two cards are accidentally sharing a rail, leaving the other rail idle. Raw system wattage (both at the input socket and delivered) would be interesting too.
I ask this because I just had a UPS failure that was causing power issues that corrupted my GPU computations, causing such a subtle failure that I wasted multiple days debugging code and not hardware. I don't know any way I could prevent this in the future except by some kind of power monitor *OTHER* than the UPS (which was the failure point.)
More details of my misadventures here. http://forums.nvidia.com/index.php?showtopic=166857
I can manually check this in the future by putting a Kill-a-Watt in series with the power, after the UPS and before the PSU, but of course that's not a solution since there's no audio alarm nor way for the computer to react (like it can from a UPS alarm.)
I suspect such a PSU with monitoring features/alarms does not exist, but I ask you experts if one does, or how I might have otherwise caught the problem.