May be Signal ground is pin 3, 5 Vdc is pin 2, 12 Vdc is pin 4, - 12 Vdc is pin 5 and shielded ground is pin 1 ??
Note: The Amiga 500/600/1200 power supply input is identical in shape to that of the Commodore C128, but they are *not* compatible. Using The Amiga:s PSU on a C128 or vice versa will most likely kill your hardware!!!!!!!