They all have a similar quiescent current, so fed from the same rail, at no load and similar heat-sinking - they should all be at an similar temp. Probably the 9V one is doing something odd - as already mentioned. making dc measurements in the presence of ac (esp at higher frequencies) can give quite amusing results. I recall ye olde worlde AVO 8 was one of the very few instruments that didn't go totally nuts when immersed in RF :P
The ripple looks OK, 100mV p-p @ 100Hz - if I am reading the scope setting right
dc