These modules will increase the recharge rate of your capacitor, but have downsides.
Passive module which increases capacitor recharge rate while decreasing total capacitor energy.
Passive module which increases capacitor recharge rate while decreasing the amount of shield restored by shield boosters.
While flux coils increase your capacitor recharge rate by slightly more than power relays, they also decrease your capacitor capacity, and capacitor recharge rate is tied to capacitor capacity. This means that overall flux coils actually increase your recharge rate by less than power relays. Only use flux coils if you're active shield tanking.