Julius the slot -tech controller has an external capacitor and will only give a boost on un regulated psu's the main advantage to fitting a capacitor is smoothing ,it helps the motor run cool and levels off the power ,Some years ago I used to sell super charger chips through Pendle slot these were merely an electrolitic capacitor in a small package which when placed across the motor connections gave a small boost to the car ,quite effective to the scx motors and the s cans we ran back then.