5v dc to 18v dc? (it can't be as hard as I am making it?)?

I need a step up transformer to go from my average bench power supply (5v dc) to 18v dc (the same I would get from 2 9v batteries). I have an associates in electronics but it's from 10 years ago and I can't make the information come back into my brain. Any help would be appreciated.

Remember you can't step up DC with transformers ! YOu need a "boost"supply. What current do you need to provide ?