The wattage a system uses is not dependent on the UPS but on the systems' specs. Like your PSU, the UPS will only draw the power needed by the system, not what the product is rated for. It is rather efficient, showing ~96% efficiency at 25% load and only gets better from there. Any noticeable increase in energy usage wouldn't be because of the UPS as it's needs are minimal.
There is one spec that I'm not finding and that is the wave form of the output. This may be important since many SMPS's that feature Active PFC require a sine-wave input and often UPS's use stepped approximation to a sine wave and in some cases they don't work properly together.
I could give you an approximation of power consumption and whether there would be a...