Michael,
Welcome to the Discussions!
I would recommend you avoid the yo-yo adapters...there is a high failure rate where the DC line from the power adapter connects to the power port plug.
The original yo-yo adapters were 45w and replaced the brick style and I believe first started turning up on the Pismo. When Apple went to the newer slimline iBooks and powerbooks, the power port plug was also slimmed down, meaning it has a smaller plug and will not connect to the older powerbooks.
If you like the style of the older "brick" adapters, you can use the PB 1400/3400/any G3/first generation iBook (clamshell) adapters; they are all 45w. However, don't buy this one:
http://depot.info.apple.com/exchange/
There are also many third-party adapters available, several having been mentioned in the past few days in these discussions. I personally like this one:
http://www.madsonline.com/