I'm not certain about this, but I would think it would depend on the motor that the toy had. They have the capacity to carry out x amount of power since it's a plug in the wall toy, but the motor would have to be able to power the toy. The wall outlet is just giving it a source to run.
The Fairy's highest speed is stronger than the Magic Wand's BUT, it's buzzier so Fairy's vibrations don't feel quite as good as the Magic Wand. The Fairy's only advantage is that it has a wheel to let you gradually increase or decrease it's strength. But I doesn't bother me at all to just use the Magic Wand on the low setting. Even though I'm a power slut, the Magic Wand's high setting isn't better than the low setting.
My response to this is that it really depends on play-style.
I like the Fairy better because you can dial it up and down. Without that ability, I couldn't "keep going" and have multiple orgasms - or it would be "orgasm torture" to do so (orgasms + pain), and that's not what I'm looking for.
Hitachi is tried, tested, and true. I think I'd actually be quite prone to using it as a body massager (it's intended purpose?) so I don't mind the strength. Relying on it as a clitoral stimulator would be way too intense, but do-able... just use sheets or towels to buffer the buzz. Also, so fun to lay on your abdomen when he's inside of you, he can feel the vibrations right through your pelvis!