I already did long stop motion videos with my A540, powered with 3V AC adapter. The A540 use only 2 AA batteries.
The SX20 use 4 AA batteries but could (note: could !!!) be originally arranged in parallel (2 pairs of AA) and needs only 3V supply. I have to check it with CHDK displaying the power voltage.
If you check it, I would be please to know

If you put 9V on his a s s e t, you will toast it
