DHT22 error

I hope someone can help me because I am at a loss for what to try next.

I built a temperature data logger using a arduino uno, a RTC, DHT22 and a sd card breakout board. When I test the whole setup on my PC using the serial monitor everything works without a problem, however when I then move the setup to where I ned to log the temperature and connect it using a 12V DC adapter my temperature reading are all 1 degC. When i connect the arduino to both the DC power supply and my PC the readings are fine, even when then disconnecting the USB and continuing on just the DC power.

Does anyone have any idea what i could do to fix this issue?

SD card modules need a lot of current, the Arduino voltage regulator, already dropping 7V (from 12 to 5) may be overheating and shutting down, do you have a 9V PS you could try?