I am currently trying to determine whether my US Vonage box, complete with a 110v power supply, needs a either a transformer or converter in order to run at 220v, or whether a simple plug adapter will do the job without frying the box. I have Googled the subject and the advice seems to be conflicting, with some indicating that a step down transformer is required, and others indicating that the power cord itself is designed to convert the voltage, without any additional conversion devices necessary. The power cord indicates designation for 100 - 240 V as well as 50-60 Hz.

Any advice would be appreciated, as I am sort of out of my element here!

Just get a US-CH adapting plug or cut the cord and put a CH plug. You adapter inside was made to work between 100-240V, if there is a button just put it on the side of the 240 if not it will automatically convert the voltage.

Did this with a laptop from the US never had a problem.

Have a UK vonage account - two to be exact, one for business and one for home use. Works well here.

I have a U.S. Vonage box and have been using just an adapter for nearly months without problems.