According to HWiNFO64 description PSU Efficiency is the ratio "PSU Power Sum"/"PSU Power".

Well this ratio seems to be not correct for two reasons

1) quite often the numerator is bigger than denominator. (ok, I know, this can be due to by incorrect measuring of input and output power BUT IN ANY CASE THIS MUST lead to a > 100 % efficency, but this never happen

2) the ratio calculated is wrong even if the numerator is smaller than denominator

Some examples of recorded values

PSU Power Sum 125,472W

PSU Power 124,000W

PSU Efficiency 89,9%

Instead the efficiency should be 101,18%

PSU Power Sum 119,089W

PSU Power 124,000W

PSU Efficiency 89,3%

Instead the efficiency should be 96,039%