Power Switch ON, not jumped: Only getting the purple +5VSB
Power Switch ON, jumped (fan sputters, then dies): purple +5VSB, both yellow cables showing +1V (caps?)
Power Switch OFF, not jumped: green cable ~2.4V, purple cable +0.5V
Power Switch OFF, jumped: +1.4VSB, both yellow cables show +0.3V (caps?)
Trying to jump the PSU again without using the power switch or re-plugging the power cable results in the fan spinning up and dying again.