I have a circuit that runs fine off USB. When I connect it to a 5V 2A power supply (a regulated switching one; an old BlackBerry charger) it intermittently locked up until I added a 220 uf capacitor (the first one I had handy).
Did I just get lucky and that was the right value, or would any higher farad capacitor work?
I have .1 uf decoupling capacitors near each chip; do I need any others?
Thanks in advance.
You pretty much in the range (highish end for me, but no issues). Unless you have a scope, you are going to have to tune by glitch. My Arduino breadboards use 100uF, while my through hole projects can go to 16uF "stubbies" and survive just fine. Greater than 16uF and Greater than 25v is the rule of thumb. Some regulators may need some turning. If you want to be precise, find Grumpy Mike and click his site 
As for the 0.1uF, I starting to think they were for the noisey 555s in the same circuit, but DuaneB could not dial the Hi-Freq out for his RC projects.
Your circuit may not have drawn enough current for the blackberry charger to function well and the cap made it more stable.
Any value from 1uF & up would likely have sufficed.
0.1uf would help with any high frequency noise, add one if you notice anything in A/D conversions, or if PWM output seems noisy when used for audio.
It is hard to have too much capacitance for decoupling but easy to have too little.
Thank you all for the information.