12V DC 3A is something you will find written on different electronic power supplies, ranging from LCD monitors and cell phones, to consoles and portable DVD players that fit in your car.
The inscription refers to the type and voltage of the current that the specific power adaptor or converter can produce. What it actually means is that it provides direct or continuous current of 12 volts and 3 Amps of power. The power supply is the small plastic box (usually black) at the middle of the power line, between your home socket and the appliance it powers.
Having 12 volt DC 3A written on your power supply means that you save a lot of energy with the new appliance you just purchased. In the old days, all of the house-hold electric devices needed 110V or more to function properly, but, thanks to advances in technology, you can now safely use any type of electronic or electric device with just the 12 volts mentioned earlier. This type of current is less susceptible to fire (by short circuits) and it proves to be more reliable, at the same time providing with a large lifespan for your device.
As far as costs go, a 12V DC 3A power supply is usually included with all appliances that need this type of current to function correctly. If your provided power supply stops working you can buy a new one for a very low price. Don't worry about it, because the expensive ones also come with expensive items and are very unlikely to break. You can find the power supply you need at the store you purchased your electronic device from or you can order it online. Either way, you will not have to spend a fortune for it.
