When two charged capacitors are connected (positive to positive): Common potential V_f = (C1V1 + C2V2)/(C1 + C2) — charge is conserved. Energy is NOT conserved — energy lost as heat in connecting wires: U_lost = C1C2(V1 - V2)^2 / (2(C1 + C2)). This is always positive, confirming energy is always lost. Maximum energy loss occurs when C1 = C2 (half the initial energy is lost). When connected positive to negative (opposing): V_f = (C1V1 - C2V2)/(C1 + C2) and the same energy loss formula applies but with (V1 + V2) replacing (V1 - V2). JEE tip: always check how the plates are connected — same polarity vs opposite polarity.