The provisions of the charter have equal force and weight as do state laws.  The only instance we can imagine of a county law having greater strength than a state law is if the county fills a gap in state law that makes so much sense that all other counties follow suit. 

There are several synonymous terms that have very specific meanings in the law: having greater strength, taking precedence, and supersede.  On 4/19/16, Geoff Neill of the California State Association of Counties, a private non-profit corporation, testified before the Mendocino County Board of Supervisors about what he had learned in the last couple of weeks about charter counties.  He clearly stated, that within the narrow scope of the charter county's home rule authority DOES SUPERCEDE state laws in conflict therewith, and then only to the extent that they are not limited by the CA Constitution.

CA Constitution Article XI § 4 (g) Whenever any county has framed and adopted a charter, and the same shall have been approved by the Legislature as herein provided, the general laws adopted by the Legislature in pursuance of Section 1 (b) of this article, shall, as to such county, be superseded by said charter as to matters for which, under this section it is competent to make provision in such charter, and for which provision is made therein, except as herein otherwise expressly provided. (h) Charter counties shall have all the powers that are provided by this Constitution or by statute for counties.

[General law county]

§ 1 (b) The Legislature shall provide for county powers, an elected county sheriff, an elected district attorney, an elected assessor, and an elected governing body in each county. Except as provided in subdivision (b) of Section 4 of this article, each governing body shall prescribe by ordinance the compensation of its members, but the ordinance prescribing such compensation shall be subject to referendum. The Legislature or the governing body may provide for other officers whose compensation shall be prescribed by the governing body. The governing body shall provide for the number, compensation, tenure, and appointment of employees.

The precedence issue is one of long debate and only applies if there is a conflict between state and county laws, i.e. spraying glyphosate on school campuses.  If the state rules that glyphosate is safe in spite of the scientific evidence, World Health Organization warnings and the precautionary principle, and the county charter has a provision banning the use of glyphosate on school campuses, then of course, the state law would take precedence, as determined by Dillon's Rule and State Preemption laws. 

Dillon was an Iowa State Supreme Court Justice, who, in 1868, during the Gilded Age of the Railroad Barons, ruled that federal law took precedence over state law, and state law takes precedence over county or city law.  California adopted Dillon's Rule in 1911. 

From Wikipedia: "The theory of state preeminence over local governments was expressed as Dillon's Rule in an 1868 case: "Municipal corporations owe their origin to, and derive their powers and rights wholly from, the legislature. It breathes into them the breath of life, without which they cannot exist. As it creates, so may it destroy. If it may destroy, it may abridge and control".[2] By contrast, the Cooley Doctrine expressed the theory of an inherent right to local self-determination. In a concurring opinion, Michigan Supreme Court Judge Thomas M. Cooley in 1871 stated: "[L]ocal government is a matter of absolute right; and the state cannot take it away""

Dillon held that local municipal governments get their derived powers from the state government, which can also take them away.  But Cooley held that governments derive their powers from the unalienable right of the People, and that power begins on the local level. 

Although the State of California has adopted Dillon's Rule and did not adopt the Cooley Doctrine, many of us clearly interpret from the founding documents of this nation that all government power is derived from the people and government exists to serve the needs of the People.  Therefore, Dillon's Rule is anti-democratic, anti-constitutional, patriarchal and obsolete. 

Mr. Neill of CSAC made it very clear that when a county adopts a charter, the law established by the charter will supercede the general laws that have been provided by the State to guide county governments.  Mr. Neill stated that there are times when charter law conflicting with general laws would take precedence in order to provide for the peace, comfort, convenience and prosperity of the county's citizens.