Nope, Life Drain only places counters; it does not do damage (which is needed in order for Plus Power or Strength Charm to add to). Here's an old Compendium example for Life Drain from Sabrina's Kadabra:
== LIFE DRAIN (Sabrina's Kadabra - Gym: Challenge Expansion)
Q. Would Sabrina's Kadabra's Life Drain be an instant Knock Out if it has a Plus Power attached?
A. No, Life Drain doesn't do damage, it just places damage counters. Plus Power only works when damage is done. (Oct 12, 2000 WotC Chat, Q136)