If you are planning to get it, and it is a 5126 model, this power adapter will work, it is 2.0a that the backlit version is rated for:

http://www.ebay.com/itm/ORIGINAL-APPLE-AC-ADAPTER-FOR-POWERBOOK-100-140-160-180-/221135710032?pt=Laptop_Adapters_Chargers&hash=item337cb72750

If it turns out to be a non-backlit version, model 5120, this power adapter is what you will need.

http://www.ebay.com/itm/Vintage-Mac-Parts-NEW-Macintosh-Portable-Power-Adapter-M5136-/351200474376?pt=US_Vintage_Computing_Parts_Accessories&hash=item51c52df508