ORIGINAL: hands without shadows
In the few psus that I have converted I have never seen a sense wire on ground, it's interesting that it's there but I see no need for it, Ill edit my write-up (again) and add that.
As far as I know all ATX power supplies require a load to function while the older AT power supplies do not, are you sure you didn't test AT ones? Please let me know so I can add that.
I would not bother with adding a comment about a ground sense wire -- in probably 1500 supplies I've looked closely at, I can only recall one -- an offbrand. I don't know why it was added or what its function would be.
The majority of ATX supplies do require a load, but some will latch without a load. I got in some of the new large fan 300W Sparkles the other day that latched without a load -- measured voltage was 12.3v on the 12v rail. However, I still recommend a preload since it helps stabilize the 12v rail when under load.
I crack hundreds of boxes a year in my work -- we keep a couple of AT supplies on the shelf for Show and Tell, but we haven't had an AT box in inventory for 7 or 8 years.
andrew