The main power supply of a FFC NMR relaxometer can be based on different topologies. Its design has been done having as a basic reference the parameters of a magnet specially designed and optimized, and the magnet current that is needed to achieve a magnetic induction of 0.2 T. Due to the particularities of this magnet, the FFC power supplies must have characteristics that are not fulfilled by the most common commercial power supplies, as FFC NMR power sources generally behave as current sources that should be able to drive cycling currents with slew rates lower than 3 A/ms. In this paper, the design and dynamic characteristics of two solutions for the power supply are presented and assessed. One solution uses an additional auxiliary power supply that is replaced by a capacitor in the other solution. To guarantee the required current slew rates, the possibility of using resistors to dissipate the energy stored in the magnet is also discussed. In addition, the performance of both topologies is also presented with attention to the fact that the resistance of the magnet is not constant‥