OK!!
There are TWO basic types of electrical voltage systems you will encounter in your modding
AC and DC
AC = Alternating Current
This type is NOT POLARIZED. Why? Because it is constantly changing direction from Negative to Positive, hence its name, alternating current. This is the form of power you get from a wall, charging a circuit. Each country has different system, Australia uses 240-250V , China around the 220v mark, check this link for all the systems:
http://en.wikipedia.org/wiki/List_of_countries_with_mains_power_plugs,_voltages_and_frequencies On the macroscopic level there are either two or 3 prongs on the standard plug that goes into your wall
A= Active Lead
E = Earth
N = Neutral
In laments terms, its the kind of Voltage you get from a wall plug, Mains Power
You use it for charging your PSP Battery and Powering your Wii. However it is only used for specific circuits, ALL circuits however can use a......
DC = Direct Current
This is polarised current, meaning it has a positive and negative terminal, this is a bit more variable then AC Voltage and is not discramenant according to the country your in, this form of voltage's most common source is the humble battery. It establishes the negative and positive components of a circuit's position (see polarised components)
This for example, IS the psp battery thats charged by your AC Voltage above
