Exclusive of any levy for the payment of principal of and interest on outstanding general obligation bonds approved in accordance with Constitution 1963, Article 9, Section 6, and exclusive of any other levies authorized by law to be made beyond charter tax rate limitations, the levy of ad valorem taxes for general municipal purposes shall not exceed two percent (2%) or twenty (20) mills of the taxable value of all real and personal property in the city. For purposes of this section, taxable value is that value determined under Section 27a of the General Property Tax Act, 1893 Public Act 206, MCL 211.27a or as may be from time to time amended.