Thanks for the quick reply,
I'm not so much concerned about the limits while being switched on, because the uno's recommended input voltage is 7 to 12v (therefore I regulated the voltage to 9v).
The part that I'm concerned about is switching it off.
Even if i used a 5v connection via the USB input it would still be affected by the slowly decreasing voltage that this PSU has during shut down.
Applying your suggestion would probably reduce the time it needs to go to 0v and therefore reduce potential damage.
I'll probably do that if it stays uncertain whether or not this voltage drop could do any harm.
(My plan was to use the empty computer casing as a lamp and have the arduinos USB port permanently connected internally so i can use the front panel USB connector to update my Sketch without opening the casing. Therefore it would be ideal not to use the USB port for power input. You couldn't know that though ;))
Thanks though regardless, I'm one step/idea closer to connecting it safely.