Del. Code tit. 8 § 516
When, by the laws of any other state or nation, any other or greater taxes, fines, penalties, licenses, fees, or other obligations or requirements are imposed upon corporations chartered under Chapter 1 of this title, doing business in the other state or nation, or upon their agents therein, than the law of this State imposes upon their corporations or agents doing business in this State, so long as the laws continue in force in the other state or nation, the same taxes, fines, penalties, licenses, fees, obligations and requirements of whatever kind shall be imposed upon all corporations of the other state or nations doing business within this State or upon their agents here. Nothing in this section shall be held to repeal any duty, condition or requirement now imposed by law upon the corporations of other states or nations transacting business in this State.
8 Del. C. § 516