PowerBook Duo power supplies come in two flavours: 24w and 36w, the latter being for the 280c and 2300c. There is a document on Apple.com that gives you the part numbers, the only way to know which is which.
A Wallstreet will boot and run from either of the two, but is happiest with the 36w one for charging etc. A Pismo should do likewise, but bring along a 36w adapter if you have one.
Pismos, however, have a reputation for needing functional backup batteries to boot (though this experience is not universal - it's not mine, anyway). This too you should check up on before "jumping" on anything, one informative discussion being here:
http://discussions.apple.com/thread.jspa?threadID=248158&tstart=946 .
I bought a Pismo a few weeks ago (with a dead 2400c) for around the price you cite. Mine turned out to have a broken hinge (which I fixed by cannabalizing some parts from a broken 12" display from a Wallstreet, which worked fine after a little filing and drilling). I suspect that the hinge broke long ago, as the machine turned out to be otherwise pretty much pristine; it was, I think, laid aside and left until I got it and bestowed a little TLC. It will now fulfil one of several roles I have for Powerbooks.
I used a Wallstreet for years, and long thought they were great machines; now that I have a Pismo, I can say honestly that it is a much nicer unit. And it will run OS8 and 9 - which some of us still prefer for some purposes to X.
