I like supercap technology, but until the energy density gets to the density by volume of normal batteries, its best use is as a secondary battery bank. For example, wind energy in areas of the US where wind can vary from calm to breezy randomly. Having supercaps get charged via turbines, then the energy from the supercaps used to feed a proper MPPT charger is probably their best use right now.
Supercaps also help as a buffer between incoming solar and a MPPT charger. It means the charger can use what voltage/amperage it needs, and still keep charging batteries until the supercaps completely discharge.
As for charging a smartphone, I can see a dedicated external battery being a great device for RV-ers who are boondocking. Plug it into 120VAC (with permission, of course) at a gas station, let the supercap array get to capacity in 30-90 seconds, then let that external battery keep the smartphones and tablets topped off for a few days of no-hookup camping.