To answer that, I can offer 2 different approaches.
TOPOLOGY
Topology is, loosely, the type of UPS mechanism. I have written in depth about this. Online and Line Interactive are the common ones. Simply, Online type is where output power is always being made by the UPS and Line Interactive type online "makes" the power if something goes wrong. So, if you want UPS to manufacturer the power output all the time, Online is the best topology. But that doesn't necessarily mean its the "best power."
OFFICIAL POWER QUALITY
Technically, power quality is the quality of the voltage; specifically, transient content and voltage magnitudes. UPSes address both problems and offer redress. No matter whether its an Online or Line Interactive type UPS, they output a voltage plus or minus their operational tolerance.
A quick check of some common units, shows some differences in Output Voltage
- APC Line Interactive 5kva (585AB) = +/- 5%
- APC Online 5kva (593g4) = +/- 3%
- Tripplite Online 5kva (to595) = +/- 2%
- Eaton Line Interactive (p5593) = +/- 8%
- Eaton Online 5kva (p9593v) = +/- 2%
So if the goal is 208volt (or other selected voltage output), the best power quality unit is a Online UPS, but with low ranges such as the Eaton or Tripplite.
But, as I have said many times, most IT equipment runs off its own power supply, and the small differences of power quality in the specs isnt worth worry about.
Worry about the quality (or absence) of your Transient Voltage Surge Suppressor.... thats where real power quality should be addressed
