The majority of pedals run on 9V and many of them can be used with a 9V battery.
But insatiable digital effects suck out the batteries at top speed or it is impossible to run them on battery.
This is when the question arises, which power supply is the most suitable one.
There are two decisive values which can be found on every power supply: volt and ampere.
If manufacturers specify a need for 9V for analog pedals, you should choose a 9V power supply.
Notwithstanding a certain tolerance of many pedals which sometimes can be operated with up to 18V, you should always check out if your pedal is one of those accepting ones.
Considering the fact that some overdrive pedals double the voltage internally, even 12V can be far too much.
In the case of doubt, analog effects prefer less voltage instead of too much.
The effect resembles a battery which is almost flat and there are some power supply that are able to control this effect continuously variable.
With regard to the value of ampere the opposite holds true: a power supply should always provide more mA than required by a pedal.
You can easily run a 10mA overdrive pedal on a 500mA power supply.
The pedal will take what it needs and nothing more.
And digital pedal which needs 250mA can be damaged seriously if it is operated with less than 250mA.
Daisy chain/ isolated
At best, each pedal should get its own isolated power supply to avoid humming or high pitch whine.
The most common reason for besides noise is a wrong or insufficient power supply.
If you lack a sufficient number of power plugs you should evade to connect analog pedals with digital effects in a daisy chain. Otherwise besides noise will be guaranteed.
If you are using a daisy chain, you should always ensure only to connect analog pedals.
And its important to consider each of them separately.
If a pedal doubles the voltage internally (Klon Centaur), it is supposed to get its own power supply.
Pedals with a positive ground (like many germanium fuzz effects) also need a power supply.
Last but not least you should keep the total output of your power supply in mind. If it reaches the limit of its capacity, it might cause a humming.
It makes sense to provide twice as much mA per pedal as needed.
This will also influence the sound in a positive way.