A family of new supplies for powering superconducting magnets was developed in our institutes. As an example, two supplies are described in the paper. One of the supplies uses superconducting, another-semiconductor-based repetitive switches. Both supplies are able to generate 1 Volt at the high-current side. Magnets to be powered by the supplies are made with Nb3Sn and NbTi wires, operate at 600 and 300 Amps, have inductances of 1.2 and 1.3 Henry and generate magnetic fields of 12 and 7 Tesla, respectively. Both magnets operate art 4 Kelvin and are bath-cooled. So far the power supplies were tested at the operating temperature using a small sc magnet as a load. Expected load curves, while ramping the current of the real magnets, are also discussed. A comparison between these sc supplies and a conventional system based on a room temperature power supply with (high-Tc) current leads is made.