I have searched on Google but to no avail. Perhaps you guys can help.
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Is there a relationship between RSSI and Power?
If so, how are they connected and does it have a formula to extract one from the other?
RSSI is in relation to the square-root of the power. See below references for the actual formula.
Holiday extra: RSSI for an RF433 module can be estimated by the time from end of transmission and noise. This is the time for the AGC circuit to increase gain from the received signal to the noise level. Please see Cosa RF433 library for an example.