The rapid growth of flexible and stretchable electronics paves the way toward compact and wearable power source devices. A shape-adaptive and stretchable energy harvester is particularly attractive due to its mobility, sustainability, and availability. In this work, a crumpled-graphene-based stretchable triboelectric nanogenerator (TENG) to harvest mechanical energy under various deformations is reported. Due to the unique stretchability of crumpled graphene structures, the crumpled-graphene-based TENGs could operate under compressive mode, stretching mode, and, more uniquely, their hybridized mode. Importantly, by shrinking a given planar graphene layer into a smaller region, a more crumpled TENG device delivered a higher output voltage, revealing the superior potential to develop smaller and better performance power generators for emerging wearable electronics. Its application as the energy harvester and motion sensor was demonstrated using finger and wrist motions.