How to build a 18volt Y power adapter cable?

[TKS]

I would like to make a power connect cable to go from my power supply to a pedal utilizing two 9 v taps wired to make the output (pedal connect end) 18 v.  How do I do this?  It would be wired in series right? 

Would this be correct?

[John Lyons]

That looks correct. Make sure to measure the plug that goes to the effect with your meter just to double check that you get 18v and that the polarity is correct.

John

[geertjacobs]

You can only use that if your power supply has isolated outputs or if your using two power supplies, right?
Otherwise you're connecting + and - together which is not good...