Hi,
A while ago, I measured the current my A1200/040 system used and got this:
Device Power @5V Power@12V
-----------------------------------------
A1200+040 2.5A 0.077A
1.4 GB HDD 0.5A
External FDD 0.7A
Scan Doubler 0.5A
CD-ROM, 52X 1.3A 1.5A
Total 5A 2.077A
The original A1200 PSU can supply +5V @ 3A and +12V @ 0.5A
I doubt your original PSU will be enough.
