Impedance matching is important especially when you are dealing with transmission lines, in order to minimize reflexions and also to really transmit the most power to the load. This is especially important in RF.
But in other types of amplifiers (such as audio, for instance) you do not need that.
Nor is it desirable, since the efficiency drops to 50% (keep in mind that you transfer maximum power to the load, but you dissipate just as much in the generator).
Power supplies are never impedance-matched. Their output impedance is to be as low as possible, to avoid voltage droop and to avoid power loss.
The output resistance of a power supply (how low it is) actually represents one of the criteria to describe how good the power supply is (the so-called load regulation).
Imagine you have a power supply and you add a resistor in series with it, effectively increasing its output resistance. Then the voltage that reaches the load is lower by an amount R*I.