To calculate the change in temperature, subtract the initial temperature from the final temperature. Example: 84.2 degree Fahrenheit - 41 degrees Fahrenheit = 43.2 degrees Fahrenheit. The temperature from morning to afternoon changed by 43.2 degrees Fahrenheit.
It needs 12 volts so it will be the standard modern power supply provides 12 volts of power.
Supposing you have a modern AC to DC power supply that operates on 120VAC and produces 28VDC at 6A. however you must consider power supply efficiency and power factor. It's not uncommon for a switching power supply to be 70-80% efficient at loads less than optimal and to have a .6 power factor.