If you don't have an internal modem on the G3, I am sure it will work.
Keep in mind a 33.6 k is on the slow side. A 56k is what all the internal modems are nowadays.
As for the power adapter - I know I have one at work, so let me check and get back to you tomorrow or Saturday.
You might be able to get a part from 3 Com which bought US Robotics.