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.
We're taking here about mains voltage (say 120 V or 230 V AC) power supplies with power ranging from a few Watts to several hundred Watts. Switch mode power supplies are everywhere; here are some pictures of their guts. The big high power components and small heat sinks are typical of SMPS. These devices are incredibly reliable, but being very often left powered all the time (even when their load is switched off), they still are the weak link.