Why not just use a regular extension cord from the wall outlet and connect the factory power cord? Perhaps they made a change, but my 4670 doesn't have a cord that detaches from the wall plug, so you can't use anything to lengthen the cord itself.
If you're trying to use something with a female connector to plug the original power cord into, then a male connector on the other end to plug into the Roku, it has to be the same size connector at both ends, just one being male and the other female.
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