Here we have an extra conversion loss but somehow it's better.
What?
The systems are on a UPS. UPSes use batteries. Batteries are DC. So, if you want to use a UPS, you have AC coming in that has to be converted to DC (to charge the batteries) and the AC power goes through the UPS to the computer, which converts it to DC. When the power goes out, the DC is taken from the battery, converted to AC, sent to the computer, then the power supply converts it to DC to run the computer.
With a DC computer, you need one conversion, AC to DC. The same DC can be used to charge the batteries and run the computer, and when the power goes out the battery can run the computer directly with no additional conversion.
So if anything the exact opposite of your assertion is true. There are either the same number of conversions (done through a central converter so you can afford a really efficient one) if you're on street power, or there are two fewer conversions and almost no loss when you're running on battery.
As for a Prius, the efficiency in those is in the fact that you can have a much smaller engine (since the electric motor and the gasoline engine can "team up" when you need a lot of acceleration) and the gasoline motor doesn't need to run when the car is moving slowly or sitting still (the battery can drive the car most of the time, and regenerative braking can reclaim a good percentage of momentum and turn it back into battery charge, so the gas motor only comes on when the battery gets low or when more acceleration than the battery can provide is needed). It's more complicated, certainly, but the whole point is to use what power the gasoline engine is generating more efficiently by storing what's not immediately used and using it later.