download and run OCCT PSU Test and see if your PC shuts down.
While running the PSU Test keep an eye on your PSU outputs of 12/5.0/3.3 Vdc. They all should be within 5% -/+ tolerance.
For instance -5% of 12 Vdc is 11.4 Vdc. So your 12 Vdc should not go below 11.4 while being tested.
Also keep an eye on both the GPU and CPU temperatures and Fan speeds.
What was the Make & Model of your previous GPU card that you said works fine in your PC.
Also post an image of GPU-Z to make sure your AMD Driver is correctly installed and to verify your new GPU card is authentic and not a fake.
NOTE: According to MSI Support you need a minimum PSU of 500 Watts so your PSU is more than enough to run your GPU card in your PC. But it could be defective and not giving out proper PSU voltages under heavy loads.
From what I have read about the reviews on your Chieftec PSU is an inexpensive (cheap) PSU so it is possible under load it is not providing the proper voltages to run your GPU card or PC as a whole while under heavy loads like gaming. just guessing though.