If you are going to replace the power supply to give a bit more grunt, then it's generally best to avoid switch-mode psu's. Use a simple linear design - traditional transformer/rectifier/capacitor. What you need is the peak current capability that the big smoothing cap gives (which may be over the steady current rating of the transformer) rather than the stabilised output of the switch-mode psu which can't handle pulse current demands very well. Watch output voltage, though, as combination of low-load output plus back emf of motors can make output transistors go pop.
Not many people build their own electronics - most people seem to stick to the mechanical bits - so good luck with it.