That's the bit I want explaining, how does it get confused with zero load, but is happy with a tiny or a huge load?
Also, how hard would it be to have a dummy load inside the PSU that was switched in if it detected the 12V was off?
They're not actually. They're twice the CIT supplies, but still quite sensible compared with non-PC PSUs.
I'm just going by what has been said by experts on stackexchange.