How to determine the power supply needed for a PCB
You add up the current draw of all the components, and then make sure the power supply can handle it.  Note that you want to add up the worst case current draw to be sure it will always work over all conditions the parts are specified for.

If this is a high volume product where reliability in extreme conditions is not that important, then you can use some fudge factor to size the power supply somewhere between the max current for all components and their typical values.  The more components there are, the lower the probability that they will all draw their maximum current at once.  These need to be different components for this statistical analysis to be valid.  Dirty Harry summed up this method well: "Do you feel lucky?  Well do you, punk?".