A powder coating composition comprising a crosslinkable composition and a catalyst system, wherein the crosslinkable composition is formed by a crosslinkable donor component A and a crosslinkable acceptor component B that are crosslinkable by a Real Michael Addition (RMA) reaction via the catalyst system, and which catalyst system is able to catalyze the RMA crosslinking reaction at a curing temperature below 140°C, preferably below 120°C or even more preferably below 110°C or below 100°C and preferably at least 70°C, preferably at least 80, 90 or 100°C, wherein the crosslinkable composition comprises a) the crosslinkable donor component A having at least 2 acidic C-H donor groups in activated methylene or methine, and b) the crosslinkable acceptor component B having at least 2 activated unsaturated acceptor groups C=C, which react with component A by Real Michael Addition (RMA) to form a crosslinked network, and wherein the catalyst system comprises a (semi) crystalline precursor P, an activator C and optionally a retarder T; wherein the (semi) crystalline precursor P is a weak base with a pKa of its protonated form of more than 2, preferably more than 3, more preferably more than 4 and even more preferably at least 5 units lower than that of the activated C-H groups in donor component A; and the activator C can react with P at curing temperature, producing a strong base (CP) that can catalyze the Michael Addition reaction between A and B; wherein the retarder T is preferably a (semi) crystalline retarder, wherein the retarder T is an acid that has a pKa of more than 2, more preferably more than 3, even more preferably more than 4 or 5 points lower than that of the activated C-H in A, and which upon deprotonation produces a weak base that can react with the activator C, producing a strong base that can catalyse the Michael Addition reaction between the crosslinkable compositions A and B. wherein the crosslinkable composition comprises a) the crosslinkable donor component A having at least 2 acidic C-H donor groups in activated methylene or methine, and b) the crosslinkable acceptor component B having at least 2 activated unsaturated acceptor groups C=C, which react with component A by Real Michael Addition (RMA) to form a crosslinked network, and a) the crosslinkable donor component A having at least 2 acidic C-H donor groups in activated methylene or methine, and b) the crosslinkable acceptor component B having at least 2 activated unsaturated acceptor groups C=C, which react with component A by Real Michael Addition (RMA) to form a crosslinked network, wherein the catalyst system comprises a (semi) crystalline precursor P, an activator C and optionally a retarder T; wherein the (semi) crystalline precursor P is a weak base with a pKa of its protonated form of more than 2, preferably more than 3, more preferably more than 4 and even more preferably at least 5 units lower than that of the activated C-H groups in donor component A; and the activator C can react with P at curing temperature, producing a strong base (CP) that can catalyze the Michael Addition reaction between A and B; wherein the retarder T is preferably a (semi) crystalline retarder, wherein the retarder T is an acid that has a pKa of more than 2, more preferably more than 3, even more preferably more than 4 or 5 points lower than that of the activated C-H in A, and which upon deprotonation produces a weak base that can react with the activator C, producing a strong base that can catalyse the Michael Addition reaction between the crosslinkable compositions A and B. <EOS>