The usage of ensure vs. insure is very important from a contractual perspective, while they sound very similar they can have very different meanings in a legal context. Insure means to safeguard against loss or damage, typically through the ... Read more
Electrical sockets (outlets) in the People's Republic of China usually supply electricity at between 220 and 240 volts AC. If you're plugging in an appliance that was built for 220-240 volt electrical input, or an appliance that is compatible with multiple voltages, then an adapter is all you need.
What you're missing is that the input is 120 volts but the output is only 12 volts. Electricity from the wall is AC, and is 120 volts. The adapter changes that to low-voltage DC, usually 3, 6, 9, or 12 volts. So the output is 12V x 1.67A = 20W, which is less than the 30W input. Output is always less than input, because the conversion process is inefficient.