As stated above, the entities form which Adam receives his powers have been altered to darker beings. When Adam says the word
Shazam, he is granted powers and abilities by these evil beings, though each aspect comes at a price. Here's a listing of said entities and their respective contributions to his power in relation to the word Shazam,
S
For the Forbidden knowledge of Stolas. Primarily a psychological and intellectual boon, this grants Adam access to a vast internal catalogue of linguistic, historical, and arcane knowledge. However, Stolas will often whisper to Adam, sometimes unintelligent, mad ravings, other times horrific arcane secrets one is better off not knowing. Adam cannot control when this will happen, except by reverting to his mortal form.
H
For the pride of Hades. Mostly a psychological boon, this aspect of power allows Adam the confidence and surety of the King of the Underworld, even in the face of insurmountable odds. However, with this pride and confidence comes egotism and megalomania, which are present in Adam's personality, but are amplified when transformed.
A
For the destructive power of Abaddon. This aspect is what allows Adam to perform feats of horrifyingly superhuman strength. The counter to this is Adam cannot keep his strength in check. Doors are pulled form hinges instead of opened casually, glasses break in his hands, and physical interaction with any human he doesn't wish to maim or kill is nearly impossible while in his transformed state.
Z
For the swiftness of Ziz. This aspect of power not only allows Adam to fly, but also to move at superhuman speeds, and to react inhumanly fast. Because of the cruse associated with this aspect of his power, each time Adam transforms, his mortal form ages considerably, ensuring that eventually Adam will be fully in Mephistopheles' service, or will simply wither away of old age.
A
For the rage of Aeshma. Calling on the undying fury of the demon of wrath, Adam is capable of shrugging off powerful blows through force of his rage alone, as well as healing swiftly any damage that manages to harm him. Using this aspect of his power, he is able to self-sustain, and will never tire or require sleep. The cost of this power is high, however, as Adam can lose control of himself entirely when transformed, entering a rage-fueled sort of fugue state. Even when not in this state, when transformed, Adam is prone to violent outbursts of temper and terrible mood swings.
M
For the power of Mephistopheles. This aspect represents the contract of Mephistopheles, and binds the rest of the aspects of Adam's power (as well as the curses that come with them) together. It fuels the eldritch crimson lightning which transforms him, as well as augmenting his other abilities. Perhaps the greatest curse of all, this aspect of his power ensures that, should Mephistopheles command something, Adam will obey once transformed. For instance, if Mephistopheles commanded the death of a specific person, as soon as Adam transformed, he would feel strongly compelled to carry out the task. This compulsion can be resisted, but only at the cost of great mental taxation, and intense physical pain.