Can you or anyone else explain how the conversion works? I'm sure I could understand it if I see an explanation, but I don't know how you convert from AC to DC.
Not to mention Killawatt accuracy, samples variance, or any possible measuring errors, IMO a ballpark calculation is still doable, even if we haven't comprehensive data about the S12II Bronze efficiency (particularly at those low power levels).
If we give a look to 80plus/ECOS certification (from Oklahoma Wolf on JonnyGuru and also SPCR findings we know that often they are already a bit optimistic), we have an 83.88% efficiency at the first test point (75W DC/89W AC) for your PSU.
Interpolating and averaging the previous S12-II 80+ SPCR findings, we should have a predicted efficiency at the same level of from 80.24% up to 81.83% for this latter: let's average and say 81.04%.
If so the difference between the 80+ and the 80 Bronze S12II could (should) be about 2.84% (at that 75W DC level).
Assuming that relative efficiencies may scale about linearly, providing that the ~21.6W DC (about the 5.7% of nominal max load) efficiency of the S12II 80+ was measured at about 65.4%, and eventually adding the previous estimated delta, the S12II Bronze efficiency should be NOT LESS than 68.2%.
Then we have a further data from Jonny Guru: the S12II Bronze (but the 520W one) was measured at 82.3% at 50W DC, about the 9.6% of that PSU nominal max load (pretty impressive): surely we also know that the efficiency ratio at a 10% load easily can be very different from the one at 5%, but IMHO we may try to do some somehow reasonable guesswork about the upper limit of a possible, predicted efficiency of your S12II Bronze at its 5% rated load level.
From the old SPCR review, we also know that the S12II 80+ 11.2% rated load level efficiency is a mere 76.3%.
The difference between the previous JG's finding (even if the load levels are slightly different) is a full 6%.
Therefore I assume that the S12II Bronze efficiency should be NOT MORE than 71.4% at around the 5% rated load level (20-22W DC).
Furtherly rounding by averaging those supposed minimum and maximum foreseable efficiencies, we can eventually suppose a nearly 70% efficiency at ~20W DC for your S12II Bronze 380W PSU.
So, if it were true, how many DC Watts do your measured AC watts match? 38W AC * .70 = 26.6W DC.
Then you have an about (at least) 1.85W DC penalty for your WD Green drive (over the Scorpio Blue), and an about (at least) 4W DC penalty for your case fans, for a total amount of aboutt 5.9W DC more power consumption.
Finally, 26.6W DC minus 5.9W DC give 20.7W DC: which I think it might be fairly in line with SPCR finding (20W DC), not to mention Killawatt accuracy, samples variance, or any possible measuring errors. What do you think?