Concentrated Strike
Only when the power crits, yes.
No, brutes and tanks do not get the instant recharge.
Stalkers do get the instant recharge on crit for Build-Up.
Comrade Smersh, KGB Special Section 8 50 Inv/Fire, Fire/Rad, BS/WP, SD/SS, AR/EM
Other 50s: Plant/Thorn, Bots/Traps, DB/SR, MA/Regen, Rad/Dark - All on Virtue.

Looking for validation: the chance for instant recharge seems dependent on activation of the power, not necessarily on hitting the target (or maybe not necessarily a live target). I noticed that a fellow player finished off a target before CS hit, yet PS recharged (and it was far from recharging on its own). Can anyone confirm/refute?
Miss Arc #147491: Rise of Bedlam
AKA Iron Smoke @Champion Server
It probably was going to be a critical, but you didn't see the numbers before the foe was defeated.
Guide: Tanking, Wall of Fire Style (Updated for I19!), and the Four Rules of Tanking
Story Arc: Belated Justice, #88003
Synopsis: Explore the fine line between justice and vengeance as you help a hero of Talos Island bring his friend's murderer to justice.
Grey Pilgrim: Fire/Fire Tanker (50), Victory
How does the concentrate strike recharging power siphon mechanic work? Does it only recharge power siphon if concentrated strike is a crit? Or is it 100%?
Do brutes get the same effect?