Many TSVs in a 3D IC are not used for signal transmission but for power delivery. Techniques needed to detect them have not been studied in-depth in the literature. In this paper, we present a test method for power-delivery TSVs, by embedding ring-oscillator (RO) based monitors (in a scalable architecture) to detect if there is any excessive voltage-drop at the end of any TSV during a manufacturing test session. One key feature as opposed to previous RO-based methods is that our approach is able to detect the worst-case dynamic voltage-drop (occurring in a very short period of time such as 1ns), rather than just the average voltage-drop over a long period of time. This is essential in order to detect small defects inside the power delivery network. These defects, if not detected, could set off a transient timing failure when the IC is operated in a system.