How to calculate how strong a power supply is sufficient? Do I need to have a supply that equals the power consumption of all the effects, even though I will never turn on all of them at the same time?
Some, if not all of the pedals, will be sucking power even when they're not turned on, but merely plugged in with the guitar. Your best bet is to sum up the milliamps (1/1000 of an amp) and get a psu that covers this figure. You may want to consider the future, when you have extra pedals, too. Going over with the current is not a problem - voltages and polarity might be.