For my power-supply micro-controller is a load. How does this load behave like? is it resistive or capacitive or inductive load?
A microcontroller's "load" varies depending on what you're doing on it. This means that if you're taking it as a resistive load. The resistance changes as the power it draws changes. This is a very hard question to answer, however I would recommend going to the specific MCU data sheet, finding it's maximum power consumption and also find the block diagram and base the load and impedance on the first block relating the the power input
A direct voltage source always thinks it's supplying a purely resistive load. That load may change, e.g. when charging a capacitor, but in this case it would see a resistance that varied from very small to infinite as the capacitor charges. For an inductive load, it would see an initial open circuit, then a resistance that decreased to the resistance of the windings as the transient proceeds