The RH10 needs 3V. But if you get the multi-volt thing, you'll be able to set it at 3V, 6V, 9V, 12V, etc., so it can be used with most things. http://www.argos.co.uk/static/Product/partNumber/9829701.htm
That's exactly what I'm using with my Japanese RH10. For my EH1 however, I use a multi-volt adapter bought from Argos for £6.99. Works absolutely fine.