Patch 7.0.3 (2016-07-19): Redesigned. Every 15 sec, your next Tiger Palm generates 1 additional Chi.
Old: Every 15 sec, you gain Power Strikes, causing your next Jab, Soothing Mist, Spinning Crane Kick, Expel Harm, or Crackling Jade Lightning/Surging Mist to generate 1 additional Chi. If you are already at maximum Chi, a Chi Sphere will be summoned near you.
Now triggers every 15 seconds (up from every 20 seconds).
Now triggers from Surging Mist for Mistweavers, but no longer triggers from Crackling Jade Lightning.
Patch 5.4.0 (2013-09-10): Will now activate from the following Chi generating abilities; Jab, Expel Harm, Spinning Crane Kick (when it hits at least 3 targets), Crackling Jade Lightning, and Soothing Mist.
Patch 5.1.0 (2012-11-27): The Power Strikes talent now grants the Power Strikes effect every 20 seconds, which causes the Monk's next attack to generate 1 additional Chi.
Old: Your Jab generates an additional Chi when used. This effect has a 20 sec cooldown.