So to update
I jump started psu.. Using 4th and 5th pin down.. That's with the latching clip facing right which should be correct I think guess having all black psu cables can be a nuisance sometimes
And connected a pump which I guess is around 10w
The pump didn't run or at least I couldn't feel any vibration from it putting my finger on it
So leaning towards yes the psu can pass self test yet still be faulty
Unless some one can definitely tell me otherwise before I go shell out £150 or so for a new psu tomorrow