I've had very few power supply failures in my life
but those that I
have had, were shorted 2N3055's used as pass transistors around 78xx
regulators. So, I have grown to not appreciate that approach either.
The normal cause of that is not providing some current limiting circuit.
The 7805 includes one (of course), but adding an external pass transistor
will negate this unless you add some more components (how to do it is
shown in the better data sheets for said 3 terminal regualtors). If you
don't and accidentally short the output to ground (or give it too heavy a
load in some other way), the 2N3055 will most likely fail. And it may