The seller should refund on that purchase, or if bought through ebay
you may be able to force the issue when it was sent to you like that.
Online sites will say if they offer refunds, as part of their agreement.
I'd seen an incidence of a different power cable used with the iBook G4
power adapter, instead of the extension cable. The original G3 White iBook
didn't have a three-wire cable ~ only a two-wire cable for AC power-in.
Your better bet would be to find a good source for new spare adapter.
I have one that was from newer tech (OWC) fits iBook/PowerBookG4..
Power Adapter for Apple PowerBook G4, iBook G4 & G3 - link to this example
..and when available, was about $25 from their site. Not just the cable.
Yet if you had no other option, to test an 'two-wire' adapter where the part
you see that is broken had no electrical connection significance, there is
a generic cord with only two-wires that can fit just the power-in port where
the missing toggle-duckhead or official extension cable would be fitted.
I've had these kinds of two-wire cables, they have a shape that fits into
the opening you see when the final connector is not in place; the item
is generally used to be sure a polarized plug is used, given that shape.
[So the generic wire/cable would go into the opening and fit most exactly.
And early adapters do not use the metal lug as a 'power ground' connector.]
My first edition G3 White iBook came with two adapters, the yo-yo round
one with different AC-in cables, and a later standard white cube Apple
adapter with only two-wires; this had the duckhead plug, also used cable.
[On this model there is no electrical significance assigned the metal button
such as is missing in image you posted; as in those, there was no wire either.]
So the power-in cable that replaces the toggle-duckhead with tiny holes
for the electrical connections inside, is what I mean by 'two-wires.' {Not the
the bigger cable in (extension) or the DC wire out of the power adapter. A
three wire AC cable has two power and one ground. The old first edition
white power adapter for iBook, has only two connectors for AC into it.
And I've seen the generic AC cord with the matching shape cast into the
rubbery plastic, these fit directly into AC-in iBook G3/G4 power adapter.
Bins of various electrical appliance cords sometimes have these cables.
{As matter of reference; while you have a better hopeful option in returning it.}
Good luck & happy trails! 🙂