The green+black pins intercept the power switch to tell the PSU when to turn on. If they were female heads, you'd just plug those pins into a second PSU to turn it on simultaneously.
Male heads? Might have come with a case with more than one power button, a daughter board, or maybe attached to a smaller special-purpse PSU (to turn on fans, water pumps, etc)
Perhaps one of those 'dual' PCs that pair a beefy, power-greedy PC with a second, light, low-power computer built in - it would allow the smaller computer to power on and off the larger one at will.
So in short, no idea