Voltage is measured in Volts, usually abbreviated to V, and most of the effect pedals need 9V to be working. Although some pedals need 12V, 18V or other voltages. A fresh 9V battery gives you 9V. Mains voltage (the wall socket) in most European countries is 230V. In USA it’s 115V and in Japan the mains voltage is 100V.
Current is measured in Ampere or milliampere which is 1/1000 of an Ampere. Both units are mostly seen as abbreviations A or mA. 1A being 1000mA is quite a big current for an effect pedal so most figures for pedals’ current draw are given in mA – milliamps, which has nothing to do with an amplifier.
AC is an abbreviation for Alternating Current, opposite to DC which is Direct Current. The mains voltage is alternating and therefore AC. There is no + nor – defined, because the polarity changes constantly with the frequency of mains being 50Hz or 60Hz depending on the country you are in. Hz is an abbreviation of Hertz used as a unit for the frequency. 1 Hertz means one cycle per second. An ‚A’ used for tuning (440Hz) is a tone having 440 vibrations per second.
Having a DC voltage source the current will always flow in one direction, from plus towards minus. A battery is a DC voltage source with a well defined polarity (the + and -). Most effect pedals are designed to be used with a DC power supply.
An AC power supply consists of one single component – a transformer. When connected to the mains the mains voltage is transformed to a low voltage. Since no rectifying is taking place the output voltage is still alternating, changing polarity. The output has no + nor -.
If a rectifier, being either one or four diodes, is added to the transformer along with a capacitor, you end up with an unregulated power supply. The polarity is now defined and the output of the circuit has a plus and a minus pole. If no current is drawn you will be able to measure the power supply’s idle voltage at its output. When you connect it to for example an effect pedal the current begins to flow. This will result in a voltage drop at the power supply’s output. So, the output voltage of an unregulated power supply depends on the amount of current you draw from it – the higher current, the lower voltage. A battery is an unregulated power source and so is a BOSS adapter of the ACA type.
A regulated power supply consists of a transformer, rectifier and a capacitor like the unregulated one. On top of that or actually at the end of the circuit you will have a voltage regulator. It’s an integrated circuit (an IC) which makes the output voltage stay at the same level regardless of the current drawn from the power supply. A BOSS adapter of the PSA type is a regulated power supply. All CIOKS power supplies are regulated. It means that no matter if you draw 10, 50 or 200mA from the power supply the voltage stays 9V DC. Of course, if you overload the power supply or short circuit it the voltage will drop. That would be the case with all power supplies types – AC, DC, unregulated or regulated.