The blooming market of portable and wearable electronic devices has triggered research interest in energy storage devices that combine both high performance and attractive form factors. Planar supercapacitors are considered as favorable alternatives or complements to batteries, especially to serve as highly flexible, environmentally-friendly and high performance energy storage devices for portable and wearable electronics. In this work, a scalable and printable method was developed to fabricate flexible planar supercapacitors. By using a cost-effective inkjet printing technique, novel and unique hierarchical Nickel (Ni)@Manganese dioxide (MnO2) nanocoral structures were constructed as the interdigitated electrodes on flexible substrates. The as-fabricated flexible all-solid-state planar supercapcacitor achieved an areal capacitance of 52.9 mF cm-2 with enhanced specific power and energy, and such a performance parameter is among the highest in literature for the same category of devices. More interestingly, the inkjet printing technique realized pattern designs with excellent versatility and working supercapacitors with various artistically designed patterns are demonstrated here. Meanwhile, the high scalability of such printable method was also demonstrated by fabrication of large size “power papers”, which successfully served as energy storage devices in wearable self-powered system to power up light emitting and gas detection devices.