Smoking arduino board -- question about DC Power supply of Arduino UNO

Hi guys,

Currently i am doing a project on Peltier device with Arduino. When i try to connect the Vin pin of the Arduino board to the 220V AC to 12V DC Converter (rated 12V30A) (at the same time the usb port connect to my computer), the arduino board immediately smoked and then i shut down the power.

I would like to ask can i use the DC converter to power the arduino? How much current will the Arduino draw? Is there anything wrong in my connection? I am afraid that the power is too high that will damage the arduino.

Arduino UNO
H-bridge 12V12A per output port, 4 ports in total
2 x Peltier device 12V12A
Fan 12V
LCD screen
Sensor DS18D20
220V AC to 12V DC Converter (rated 30A)

The connection is:

12V DC Converter →H-bridge →2 Peltier & Fan
└--→Arduino →Breadboard→ LCD & sensor

signal input to control the H-bridge

12VDC is fine. Max. total power draw for Arduino board is 500mA but if the current exceeds 200mA, it is better to use 9V otherwise the regulator will get hot.

USB and power together is fine.

Your connection looks good. High power consumption devices are powered separately, that is right way.

Blue magic smoke? Something has gone. Regulator? Test your Arduino separately. Disconnect all and then.
Is your DC power supply ok? 12V and DC? Really?

There are some white smoke immediately after I switched on the power supply. The ardunio board became very hot in just 2 second. It was then no longer usable(when i power it by usb port only, LCD screen on, but display nothing, and the computer software can't detect the arduino).

The DC power supply is bought from TAOBAO and i used multimeter to test it already. the output is around 11.9V DC.

Did you connect it backwards by any chance? That'll make smoke, especially if you connected to Vin and Gnd, instead of using the barrel jack (which is protected against reverse polarity, at least in official boards)

You should absolutely be able to power Arduino off 12v external supply (though if you're pulling a lot of current from the Arduino's 5v rail, as Budvar noted, the regulator can overheat)

The voltage is good. Probably short circuit. The regulator or something in the circuit around it is frequently destroyed, also MCU can be destroyed. I don't know if it worth for repair or better to buy a new one. It depends on your skills. Fortunately the UNO is cheap.
It is lecture for you. Check the circuit carefully first and do particular tests of functionality.