So i want to buy some effects from the US, mainly an ibanez tube screamer, but i don't know whether they will work on my power supply.

if i have an australian 9V power supply will it work in the pedal without stuffing up the pedal, or will i need a transformer to use it?
Assuming the DC in jack on the pedal is the same, which I don't see why it wouldn't be, then yes it'll work. The supplies will both put out 9V. It's just the power from the wall and shape of plug which is different. Make sure to check the polarity of the DC jack and your power supply though.
It'll work fine. 9V is 9V, doesn't matter where the pedal is from.
If you were using an American power supply then you'd have a problem, but you aren't.
It's fine, just make sure you've got an Austrailian 9v power supply that's the same polarity and socket as on the pedal.

"Show me war; show me pestilence; show me the blood-red hands of retribution..."