Among their claims about his spending, they say he paid hundreds of thousands of dollars to employ a sound engineer to read him his lines on film sets.
The actor has used the method "for years to feed him lines during film production", according to a court document that was filed on Monday.
"Depp insisted that this sound engineer be kept on yearly retainer so that he no longer had to memorise his lines," according to the papers, written by attorney Michael Kump on behalf of The Management Group's Joel and Robert Mandel.
A lawyer for the movie star responded by describing the allegations as "psychobabble".
A statement from Adam Waldman said: "This is how guilty people respond when confronted with the detailed results of a nine-month legal and forensic investigation conducted by four firms."
In the new document, The Management Group (TMG) said the Pirates of the Caribbean star may have "compulsive spending disorder" and needs "a mental examination".
He originally sued them for fraud, but in an amended complaint filed on Monday, the firm said they "did everything possible to protect Depp from his own irresponsible and profligate spending" before he fired them in March 2016.
According to the reports, they claim he spent more than $75m (£58m) to acquire and improve on 14 residences, including a chain of islands in the Bahamas, multiple houses in Hollywood and a 45-acre chateau in the south of France.
They also say he bought 45 luxury vehicles, 70 collectible guitars and enough Hollywood memorabilia to fill 12 storage facilities.
Depp spent up to $1.2m (£930,000) a year for a "personal on-call physician" and "millions more to employ an army of attorneys", they allege.
They say the lawyers bailed him out of legal crises and made a series of "hush money settlements" - details of which will be revealed if there is a trial.
And they dismissed as "laughable" a claim by a lawyer for Depp that he spent $30,000 (£23,300) a month on wine as an "investment".
"Depp would be hard pressed to find a single bottle of wine that he purchased during his tenure with TMG that he or his various companions have not yet consumed," they said.
"Wine is not an investment if you drink it as soon as you buy it."