How to get a dc power supply to produce 2V at 10-20 milliamps?

What brand and make is the power supply?
What kind of load are you connection this to?

 

What resistor would you expect to connect across 2V to pass 20mA?

 

You don't need a power supply, you need an opamp.

 

But you can ONLY get a 2V source to produce a current of 20mA through one particular value of resistor. If you have an open circuit at the terminals then the current will be 0mA. The supply can't 'insist' on any value of current.
The current depends upon the Load and the Supply Volts:
I = V/R

Perhaps you should specify a bit more about the circumstances of the OP. I have a feeling there is something else we should know.