We have designed and constructed a new microprocessor-controlled power supply, which is needed to excite the required multipole fields within three magnetic twelve-pole elements. We require the multipole fields to align and focus an electron beam and to correct the aberrations of an electron spectrometer which is mounted on a Cryo-STEM. With this power supply, the strength and orientation of each multipole field can be controlled independently. In order to reduce the number of digital-to-analog converters, we used a dynamic refresh technique to provide the analog output voltages. As an additional benefit of using a microprocessor, the number of front-panel controls could be kept low and extra functions provided, which would be difficult to implement in an analog system. The use of dynamic refreshing to produce analog voltages is not new, but the results obtained from our system indicate that the technique may also be employed where high stability is required.