This work presents a fully configurable smart power unit suitable for kinetic energy harvesting transducers, enabling self-sustainability for wearable devices. The proposed power management circuit hosts a low power microcontroller to manage the energy harvesting, voltage conversion from batteries, and wake-up circuits to exit low power states automatically. The source and the load power points are decoupled with multiple DC-DC converters aiming to supply loads with adaptive voltage scaling and high reliability. Experimental results using commercial micro-kinetic generators show the flexibility and efficiency of this approach: the proposed power supply unit achieves a quiescent current of 57 nA and a maximum load current of 300 mA, delivered with a harvesting efficiency of 79 %. We evaluate the proposed system with commercial kinetic energy harvesting transducer generating 4.26 mW when worn on the ankle during walking.