Source -Google
We still don't have an explanation from the DCEU, but we do from the comic books.
IMAGE SOURCE -Iig
The same abilities that belonged to Hercules, Atlas, Solomon, and Zeus were all present in Black Adam.
IMAGE SOURCE -Iig
The word Teth-Adam and Billy require to acquire their powers or give them away is "S.H.A.Z.A.M.," which is the name of the heroes and gods that spell it.
IMAGE SOURCE -Iig
Black Adam clearly had the upper hand.
IMAGE SOURCE -Iig
Black Adam's powers only grew in later comic book renditions.
IMAGE SOURCE -Iig
Although Black Adam ought to be Shazam's equal, some of his skills are beyond Billy Batson's grasp.
IMAGE SOURCE -Iig
Black Adam can only be defeated by Shazam by using his inventiveness from childhood to dupe the antihero into saying the secret phrase that will restore his powers.
IMAGE SOURCE -Iig