I have a pedal that is 12v at 400mA. Looking at a Voodoo power supply that has some 12v 1200mA max outputs. So okay  to use for my 400mA. Do these power "downward in mA safely, or do I have to match it exactly???  
 
ps..wow, what needs 1200mA ?

Your fine. You have 15 AMPs in your wall socket too but you only use a tiny bit of that when you plug in the Power supply. 
Most important is a steady clean voltage which should be regulated in a quality supply. That's why it's not recommended to use cheap generic power supplies, they are never regulated. 
The pedal will just use what it needs. The reason it has a high output is so it can power up more than one pedal. 

Just what I needed to know . Thanks