Etherwave power supply problems

I live in the UK and have the 2 pin plug for my Etherwave. I just plug this in to the standard UK socket and it works fine. I recently played my first live gig with the Theremin and had a situation where I just couldn’t get the any sound from the unit. I tried various sockets and had no luck and then all of a sudden it just worked fine. Has anyone else had similar problems?

Thanks

it might be safer with a two to three pin plug adapter, available from Boots , Dixons etc for a couple of quid