Single-phase inverters and rectifiers require the use of an energy buffer to absorb the twice-line-frequency power ripple present on the AC side. Historically this challenge has been addressed by the use of large electrolytic capacitors. However reliability constraints and the need for improved system performance have motivated designers to seek other capacitor technologies such as ceramic and metal film which are frequently used in conjunction with active filtering converters to reduce the volume of required capacitance. Active filtering converters cycle the capacitor voltage over a wide voltage range while maintaining a constant DC bus voltage. This large-swing operation is very different from that of most other filtering applications, and the data sheet parameters available for commercial capacitors may be ineffective or require special care for calculating characteristics such as efficiency and energy storage capability. This work presents an experimental setup for evaluating capacitor performance under a large voltage swing. Energy storage data for several capacitors in the 50 V to 450 V range from several manufacturers is included. The approach and findings of this paper can serve as an aid to power electronics designers for the selection and evaluation of capacitors in energy buffering applications.