When do you get around to designing the power supply for your new product? Before, after, or during product development? Whatever your approach, you probably need an ac-dc supply, perhaps with some dc-dc converters, to provide some of the multiple dc voltages needed in a sophisticated design.
It used to be so easy. All it took was a step-down transformer, a rectifier, and a big filter capacitor followed up with an IC linear regulator. This is no longer possible as power-supply requirements have become tougher over the years. Today’s power supplies must be super-efficient, generate minimal EMI, meet stringent regulations, and affordable.