You probably had power hooked up backwards if I read your post right. The early PB had a 2-contact "barrel" plug, center POS 24V, outside NEG. Wallstreets and later G3s use a 4-contact plug like a stereo headphone with an added outer shield like an RCA plug. The wiring on the plug is, TIP=ADB data for smart charger/battery, RING=NEG, SLEEVE=POS 24V, SHELL=GROUND (usually connected to NEG inside laptop). iBooks use a smaller 2.5mm version of the 4-conductor plug with the tip hooked to the green and orange LEDs. Since the sleeve is the last contact to enter the socket when you insert a live plug, it is the "hot" one, not the tip as you might expect.

If you do replace a broken plug on your AC adapter with a stereo headphone plug, be sure to insulate the sleeve from the outer shield of the laptop or you'll have a short. The outer shield contact isn't required for operation, and the most common failure of Apple's AC adapters is the wire fraying and shorting where it enters the plug.