FYI, I did some additional testing: http://audiosciencereview.com/forum/index.php?threads/measurements-of-sonore-microrendu-streamer.577/page-34#post-18202
Bottom line, combination of iFi Power and microRendu are responsible for creating mains related distortion products that are not there otherwise when microRendu is tested without iFi iPower and iPower is tested without microRendu. iFi’s theory that all of this due to measurement error I am afraid does not hold water based on my testing as the measurement system remains the same in all of these scenarios.
Answering a related question, no, I don’t think these mains distortions are audible. While they are 30 db higher than what the DAC does without, they rise up to -90 db or so in low frequencies where our hearing systems is least sensitive.
Should you use it otherwise? I wouldn’t. There are a lot of choices in power supplies. If you are spending this much money, spend more and get a linear power supply to power microRendu. It is your money and I feel free to spend it for you. 
Last but not least, while the iFi iPower has gotten all the attention, it is really a side show. The bigger message from my measurements which no one has disputed at theory or otherwise is that even when using linear power supplies, no fidelity improvements are seen whatsoever. The noise floor does not change. Such a noise floor was thought for sure to be lower in countless arguments until I did my testing to dispute it.
Now there are theories of dynamic noise floor but yet again no data is there to show such. The designer and manufacturer has not made any such measurements either, no is there any design implemented in there that specifically addresses this issue. It remains wishful thinking that this benefit exists.
And kudos to whoever said that if you have high fidelity USB DACs, it better darn well not be sensitive to vagaries of USB input. To think that such a DAC designer is not competent enough to accomplish this, but the designer of microRendu was using a couple of regulators and clock modules, is able to do so, stretches imagination far beyond where I want to go.