Question on my DIY power supply...

[ACS]

So, I've got a non-regulated wall wart, rated for 12V @ 500mA (6VA).  I'm running this into a 1A 7809 (with a 470uF cap to ground pre- the regulator and a 10uF to ground post-regulator).  Getting a very nice quiet, consistent 9V which is great...

But, I'm trying to figure out how many mA this should be capable of putting out - and find myself going around in circles!  Or is it irrelevant, and would I just start to experience voltage sag on both sides if I try to pull too much current?  Given that these things typically need in the order of 2.5V over output voltage to maintain regulation (which is pretty much the 12V in) does that just mean the max I'd get would the 500mA anyway, as below 12V it would start to sag?

Or I guess to be more accurate, using 11.5V @ 6VA, I should be able to draw 6/11.5, or 522mA from the wall wart before it starts to drop below 11.5 V and the regulator can't keep up.  But then, does Ain = Aout??

Aarrrgh!  Someone put me straight on this - it's doing my head in!

[petemoore]

  12v 500ma WW.
   Seems the regulator is depicted as 1A [or double the WW's current output].
  The 'worry' would be heat dissipation from the chip [heatsink?], with the regulator operating nicely, the voltage should be a very 'stiff' rail, no sag, almost no ripple.