I’ve seen personal blender motors with anywhere from 150 to 1700 watts of power. Anything below 450 watts probably won’t actually liquefy ingredients, which isn’t necessarily a bad thing for things like salad dressings and sauces but which probably isn’t the best for smoothies. From 450-900 watts will liquefy the ingredients, but it may have issues with small or tough ingredients like seeds and root vegetables. Anything above 900 will likely liquefy anything put in there. The higher you go above that, the faster the liquifying process will occur.