When we want to use some pedal effect, between our guitar and amp, we usually don't put attention to voltage and current stuff. We just plug the pedal, check it and, love or hate it. But... are we hearing the pedal as its best?.
Batteries / DC Adaptor
Most of pedals are designed with a constant DC current / voltage in mind. That means that the best way to know if a pedal can deliver what you are expecting from it is to test it with batteries first.
Your mains (as in my case) can be inconsistently delivering voltage and current and, very few pedals are being made with a subsystem that helps them to internally regulate such fluctuations.
So, if you wanted to know if that pedal is for you, please, try it with batteries first.
After you've tested it with batteries, you would probably want to run this pedal with some DC Adaptor, to avoid the typical case were your can run out of battery because you leaved plugged your jack in its input. Or you would like avoid the case of running out of battery in the middle of a performance, specially if that pedal isn't a true bypass one (which can completely shut up your guitar).
But, since mains voltage and current are so variable, your DC adaptor will provide variable outputs, your pedals will receive variable inputs and will deliver variable sounds, from full bodied and musical ones to, thin, trebbly and weak ones.
There are some kind of pedals that work best with lover voltages than the nominal one. This is the case of vintage germanium fuzzes, that seem to deliver a better sound when used with old worn batteries.
There are some other pedals that can sound really enhanced with higher voltages at their inputs. Usually, boosters, overdrives and compressors can open their sound and have better dynamics and headroom at higher voltage levels.
There are other pedals that simple don't seem to be enhanced with a higher voltage than the nominal one but, since the nominal voltage is often not reached (because of fluctuations of your mains) they just don't deliver the right sound.
When moving from batteries to DC Adaptors, it is time to carefully study your needs and to plan your pedal board needs.
Planning your pedal board needs
If you are going to use some DC Adaptor, it is a must for you to carefully read the technical specifications of every pedal and, tech specs of your DC Adaptors, as well.
Every pedal needs a minimum voltage to properly operate and, have a maximum voltage they can receive to not damage the unit. Some pedals can run just at 9V, like the Strymon El Capistan or the Dry Bell Vibe Machine or, those Weehbo pedals that have the Dynamics Switch (which doubles internally the voltage).
Most pedals will allow a voltage input between 9V and 12V or, between 9V and 18V.
Every pedal drains a maximum amount of current (expressed in mA) and, that max current will depend on the voltage so, when you increase the input voltage, the drawn current increases proportionally.
Every of your DC Adaptors can deliver a maximum power, with maximum current on its output (or outputs).
You MUST be sure that every pedal is being feed with the right amount of voltage and current and, that you aren't overloading your DC Adaptor, demanding more power than it can delivers.
Practical Case example
You know, every pedal board is alive and, pedals enter and exit constantly. At a certain point of time, a single DC Adaptor wasn't enough to run my heavily loaded pedalboard so, I am currently having two Voodoo Lab Pedal Power 2 Plus units and, therefore, I am planning my voltage / current needs with the help of both units, which I try to balance in the best possible way.
If you read the tech stuff of that Pedal Power 2 Plus Adaptors, you will get more or less the following basic information (after a big headache trying to understand everything together).
There are three groups of outputs: 1 - 4, 5 - 6 and 7-8.
All work the same when the micro dip switch is on its "normal" position for each entry. All them will deliver 9V.
What makes them different is that groups 1-4 and 7-8 will deliver a maximum of 100 mA, while the group 5-6 will deliver a maximum of 250 mA.
So, if you have a pedal that drains more than 250 mA (as some synthesized units) you will never get a good result with this Adaptor, you will need to go for anything else (Voodoo Lab has one more unit, specifically for this, able to deliver 500 mA by output). By example, the Carl Martin Octaswitch MKII cannot be feed with any Pedal Power 2 Plus unit.
As I said, there are pedals which sound can be enhanced by running them at higher voltages.
The Area 51 wah it's recommended to be feed at 12V, as the Weehbo Bastard.
I know there is some improvement in openness, definition and dynamics in other pedal types, as the Wampler Decibel+ or the Wampler Ego Compressor, at least, because feeding them at 12V ensures that at least 9V are reaching their inputs.
But, if you plan to increase the input voltage, make your maths before and plan a proportional current drain.
If the pedal drains 30 mA @ 9V, apply a proportion rule and you will find that it could potentially drain (at least) 40 mA @ 12V and 60 mA @ 18V.
So, first step is to know each pedal specifications and see what each pedal requires for your needs and see how those needs can be covered with your DC Adaptor (or adaptors).
This is the excel sheet I was using to plan my own pedal board needs, with all those pedals I've currently having there and those foreseen in a near future.
At header, the output voltage and max current by output in each Pedal Power 2 Plus unit, when using their outputs in "normal" mode, delivering 9V.
Those values change when the DIP switch is switched on, for each particular group.
In the case of the group 1-4, the max current drops to 60 mA and voltage steps up to 12.3V by output.
Below, the detail of each pedal, with its max drain value at the voltage I would run it, expressed in the last column (9V or 12V). The middle two columns (Unit A, Unit B) are the assignment of each pedal to each particular output of a particular unit. The two following columns are assigning the max current load for each unit, which total "load" can be seen as totals on the summarizing line at bottom.
You can see that one of the Pedal Power 2 units is using all their outputs and, that the second unit is feeding just three pedals but, even this, the "load" of that second unit is still higher than in the first one (390 mA against 377 mA).
In my planning, I am first allocating the big stones and, the bigger stone here is the Strymon El Capistan, which needs 250 mA, just the maximum current a Pedal Power 2 Plus can deliver in a single output. This level of current can be achieved in outputs 5 or 6, only. I've assigned output 5 of the second unit (physically closer to the pedal) for this.
There are four pedals I wanted to run at 12V. Any Wampler pedal will deliver a good sound if you can at least feed them with 9V and, all them allow voltage levels up to 18V.
To feed them at 18V means that two outputs of the Pedal Power 2 Plus unit should be allocated for each single pedal but, switching on the DIP switch of each required output for group 1 to 4 will deliver me 12.3V with a single cord and a single output.
Therefore, I've switched on DIPs for outputs 3 and 4 in each unit, to run my pedals at 12.3V.
You can see that the Area 51 Wah was assigned to output 3 of Unit A, Wampler Decibel+ was assigned to output 4 of same unit, Ego Compressor was assigned to output 3 of Unit B and, Weehbo Bastard (to come) was assigned to output 4 of same unit.
Then, I've started to assign each pedal, beginning with the "weighter" ones (more current drain) and, ending with the "ligther" ones, until I've got an acceptable current drain balance for both units.
The total maximum current is 767 mA (0.767 A) so, I should be sure also that the extension sockets rule has a cord that can support such a current and that the output of the Phonic PC9000E power conditioner can deliver such an amount of current.
Sure, if you use just batteries, you can completely forget all this but, if you need DC Adaptors, be sure you are planning the marriage of each pedal with the right Adaptor output, to get the best from your pedalboard.