To control thermal runaway in PCIe, SATA, and similar interfaces, the maximum drawable power from a slot is limited. The increasingly bursty load (including CPUs, ASICs, motors on HDDs, etc.) on the PCIe/SATA slot demands such power that the electrical design power (EDP) can be much larger than thermal design power (TDP). When this happens, the slot power specification can limit the performance of the load, and the datacenter power supply design needs to be overprovisioned for the EDP, if it can last long enough. This disclosure describes techniques of local energy storage that enable riding through EDP power excursions without additional provisions for upstream power or hitting the limitation of the slot. Local energy storage is realized using an active capacitor comprising a bidirectional buck-boost DC-DC converter and a large capacitor. In boost mode, the capacitor is recharged to store energy. In buck mode, the capacitor is discharged to supply power in parallel with the main rail. Local energy storage enables the provisioning of power equal to the TDP, while avoiding overprovisioning and associated costs so as to optimize the performance for total cost of ownership (TCO).

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