For most home devices it is not a standard voltage 220 AT, and all 12. This voltage LED lamps, fan, tape recorders and amplifiers, zaryadok and some laptops, kitchen appliances and much more. Almost all homemade rated for 12V, поэтому получить заветное напряжение бывает достаточно важно. 
When you can spend a little.
When it comes to long-term operation, then look for a workaround is not necessary. It will be easier to buy a power supply, and use it. So, We will approach the industrial power supply. These blocks 12B are at the output, but different power, that allows you to choose the right balance volt-amperes accurately. You can find inexpensive laboratory power supply, where the parameters are set outgoing current, but it can hardly be called a constant source of power.
Buy something new is not always necessary. Ranko boo technology will always find something cheap, with the power supply system, which gives 12V output cherished. It may be tape, especially cluster - they are not wanted, and you can get a very cheap. The old technology is set down transformer or another transformer - it is exactly what we need.
If you pick out the inverter from the old equipment would not be desirable, you can buy a transformer itself. The Chinese are a dime, that Ali, that we have in stores. But we must remember the price - the lower it, the lower the power of such a device. Paul amps or 0,7 are available for 20 hryvnia, 10-12 for 100 UAH and so on in ascending order. It is certainly cheaper, than ready BP, but also the safety of you no promises.
If you do not want to spend money.
As a temporary option and without cost, You can use those devices as a power source, which is already in the house. For owners of stationary PCs - they already have a source 12 Volt. The only problem - to calculate power. Manufacturers indicate the general, it is the average unit 20+ Ampere. But a separate connector may provide somewhere around 4-5A, It depends on the source of power and a consumer.
If you do not know, a current of your device, You can use a multimeter or clamp meter for measuring. But to use them, not all are able and good, precision instrument worth the money. To measure at home, you can use a portable electricity meter without the use of measuring instruments. Many of them are counted not only current consumption, but also the power of the device. So, model Lemanso LM669 It can show the load in real time.
