If you have a b adapter with a low A or mAh output, and if it works the adapter is likely to be too hot and can be dangerous, your device is unlikely to be powered.
What about watts?
Voltage carries power and amps is a measure of how much power it consumes, think of it as a river, how wide the V river is and how fast it flows, so the open frame SMPS circuit of a low voltage is a small river flowing fast.
If we look at the river, we can calculate how much water is flowing in the river in an hour. It will be vats. There is a direct relationship between these three variables.A 12 V2 adapter (12 m river flows 2 hours per hour) will have 12 x 2 = 24 W watts.
Here are the basic equations
• W = V x A
• A = W / V
• V = W / A
Most devices will list A or MAH and will not list watts even if you have one but need to use the original equation to convert to another.
Read connector polarity
Once you have the V and A down, then comes the hard part, most devices have a circular connector, which has one pole and carries another hole.