I bought a special cord at my local Sew & Vac [LQS and more] that has a foot pedal for speed variation. I plug my LA bobbin winder by Alphasew into this cord and then plug this special cord into my surge protector. I can now adjust for speed when winding my bobbins. I love it. Especially since the newer LA [and other] bobbin winders with built in speed control are so expensive.
Not sure how this would work with sewing machines ... but??? It didn't cost all t hat much as it is great for this use.
ali