They'll still steal a fixed amount based on the talisman (the 3 that Kaz noted above), they'll just only do the steal check once for a set amount, instead of potentially multiple times.
Askora described it right, but as another example, right now if you use an AoE basic with Energy Talismans against 3 enemies, you may steal 0, 3, 6, or 9 Power with that attack (and it's
more likely than advertised to steal at least 3 Power); after this update, you'll steal 0 or 3 Power, and the chance of stealing Power will actually be 45% (not potentially more based on the number of enemies hit).