How to factory reset dead Apple iBook G3/366 (Firewire/Clamshell) to sell?

Without power to the iBook, the only way to erase/wipe the internal hard disk would be to open the computer and remove the drive. This is not quite easy. You may find details if you search for the computer model and something like disassembly or replace hard drive. The removed hard drive can then be connected to a universal USB bare-drive adapter, which in turn would be connected to the USB port of another Mac (or PC, with the appropriate software) for wiping.

It would be easier with a working power adapter. If you take a look at the text on the M7332 (a magnifying glass may help), you will find that it has a DC output of 24 V at 1.875 A (max) = 45 W. It has a 9 mm outside diameter DC plug. This is a special plug (with an internal pin that looks like a 3.5 mm stereo plug), not to be confused with a standard barrel-style plug. You may be able to find a used power adapter via an online auction site, but the condition would be unknown.

A normal/universal power adapter with a 24 V DC output (at approx. 2 A) with a standard barrel DC plug cannot be used directly. A special adapter piece converting a standard barrel plug output has been known to exist (a web search for something like 9 mm iBook DC power plug adapter?).