Power electronics losses (in watts loss per watts delivered) can be well-approximated as having a constant term + linear term + quadratic term. If the load is

Power electronics losses (in watts loss per watts delivered) can be well-approximated as having a constant term + linear term + quadratic term. If the load is very low, then the power delivery equipment will still be spending its constant term losses, which may be large compared to the total actual load. But the PUE measurement system doesn't know how the various severs are spending power, just how much they are spending. So a busy wait, computing pi, dynamic language hash table lookups, or doing useful work all look the same.