How do I figure out the right ac/dc power supply for a modular led lighting system?

First let me say I am very new to electronics, so please forgive my ignorance.



I am trying to make a modular LED lighting system for my bookcase. It involves plugging in X number of led 'pods' into a box, hopefully powered by a ac/dc power supply. And I want to be able to plug in more 'pods' in the future as necessary.



The pods would be in a parallel array, and each pod would have 1 high-brightness led (around 3.5 forward voltage @ 20 mA). I know each led would need to be in series with a resistor of whatever size depending my input voltage.



What I am having a problem with is understanding how ac/dc power supplies work. As I understand it, they supply a given voltage (say 5vdc) if the load uses a certain current (say 600 mA). But if I add or remove some pods it would change the amount of current used by the device, and in turn raise or lower the voltage supplied by the power supply? And if I removed some pods, and it did raise the voltage, would that blow out my LEDs?How do I figure out the right ac/dc power supply for a modular led lighting system?
A good-quality supply has a regulator in it so it will adjust for the load to keep the voltage constant. One that supplies USB-style power for example (like a cellphone charger) would be regulated.



An unregulated supply will make roughly its rated voltage, with some ripple. Under load it will not do as good a job of keeping steady voltage, but it will still be close enough for this simple task. It will be cheaper.



So, you could use a 4.5V %26quot;wall-wart%26quot; cheapie. Measure its output at no-load then size the LED resistors for that voltage. Then the only thing that will happen is your other LEDs might dim a bit as you add more of them.