Psychic Transfer

• WWizards of the Coast2008-08-01
  Official Ruling
  If one of the players has a negative life total, you use their actual life total for determining the difference. If that difference is five or less, then the other player receives the negative life total.
• WWizards of the Coast2011-01-01
  Official Ruling
  If an effect says that a player can’t lose life, that player can’t exchange life totals with a player who has a lower life total; in that case, the exchange won’t happen.

Rulings via Scryfall