I've only heard the term "blanket charge" used to mean a lump-sum fee.
"I went on a weekend cruise and all of the food, drinks and airfare, were included in the blanket charge of $1000."
I can tell from the context of your other example,
The blanket charge is often made by TNOJ purists... that it is referring to an alternate meaning of the word charge.
Charge has many meanings, see below.
To simplify your example:
"The blanket charge is often made by TNOJ purists and others that Dixieland jazz was merely the white musicians' watering down of the black players' TNOJ."
- blanket charge = accusation
- TNOJ = a New Orleans Jazz Music
- Purists = a group who dioesn't like change
- watering down = oversimplifying
"The black musicians accuse the white musicians of oversimplifying jazz music."
CHARGE (as a NOUN):
- a price asked for goods or services. ("an admission charge") - synonyms: fee, payment, price, tariff, amount, sum, fare, levy
- an accusation, typically one formally made against a prisoner brought to trial. ("he appeared in court on a charge of attempted murder") - synonyms: accusation, allegation, indictment, arraignment
("he pleaded guilty to the charge")
- the responsibility of taking care or control of someone or something. ("the people in her charge are pupils and not experimental subjects") - synonyms: care, protection, safekeeping, control; More
custody, guardianship, wardship; ("the child was in her charge")
- a person or thing entrusted to the care of someone. ("the babysitter watched over her charges") - synonyms: ward, protégé, dependent
- a responsibility or onerous duty assigned to someone. - synonyms: duty, responsibility, task, job, assignment, mission, function; ("his charge was to save the business")
- an official instruction, especially one given by a judge to a jury regarding points of law. ("the judge gave a careful charge to the jury") - synonyms: instruction, direction, directive, order, command, dictate
the property of matter that is responsible for electrical phenomena, existing in a positive or negative form.
the quantity of matter responsible for electrical phenomena carried by a body.
energy stored chemically for conversion into electricity.
an act or process of storing electrical energy in a battery.
informal: a thrill. ("I get a real charge out of working hard") - synonyms: thrill, tingle, glow, excitement, stimulation, enjoyment, pleasure;
- a quantity of explosive to be detonated, typically in order to fire a gun or similar weapon.
- a headlong rush forward, typically one made by attacking soldiers in battle. ("a cavalry charge") - synonyms: attack, assault, offensive, onslaught ("an infantry charge")
There are also different meanings as a VERB.