Electro-adhesion (EA) is a low-power, tunable, fast and reversible electrically-controlled adhesion method, effective on both conducting and insulating objects. Typically, only the electro-adhesive detachment force, i.e., the force required to separate an object from the EA patch, is measured. Here, we report a method that enables comparing the pre-contact EA attachment forces with post-contact EA detachment forces. We observe that pre-contact pressures are 1 to 100 times lower than post-contact detachment pressures, indicating the large role played by surface forces, charge injection, and polarization inertia. We characterize the time-dependence of pre- and post-contact EA forces as a function of the applied voltage waveform, observing that using an AC drive allowing for much faster release than DC operation. We measure both EA forces on conductive and insulating objects, using over 100 different EA patches covering a wide range of electrode dimensions. At 400 V, the EA release pressures for conductive objects range from 1 to 100 kPa, and are 1 to 10 times higher than pre-contact adhesion force. For dielectric objects, release pressures are 1 to 100 higher than pre-contact adhesion pressures. The methodology presented in this paper can enable standardized EA characterization while varying numerous parameters.