I just ordered the MTX Ultra and it is on its way and I am trying to get prepared for its arrival. It doesn’t come with a power supply and it specifies a 9V center negative power supply. I stopped in to a shop to find a power supply and the guy recommended a TrueTone One Spot. It looks like it will work but there is nothing on the box that tells me if it is center negative. Does anyone know if this will work?