Tests with superimposed voltages are used as a means of of replicating the electrical stress occurring on power equipment. During these tests, the components are simultaneously stressed with either an AC or a DC voltage and an impulse voltage (e.g. LI/SI). The measurement of the resulting voltage is deally achieved with universal voltage dividers (RCR dividers), which have not yet been standardized. This publication focuses on the performance of universal voltage dividers at different voltage combinations as a proposed contribution to the standardization of tests with superimposed voltages. The measurement results of two commercially available measurement systems from different manufacturers, based on universal voltage dividers, were compared with a reference measurement system to assess the effects of composite voltages on linearity and measurement uncertainty. The investigations were focused on the combination of DC and lightning as well as switching impulse voltages. The performed tests showed that a DC component (tested up to 350 kV DC, maximum bipolar impulse stress of 1100 kV) did not lead to any effects on the impulse voltage measurement performance of the measurement systems. All systems retained their high overall accuracy during all of the tests. The obtained results will be used to investigate how universal voltage dividers can be calibrated and how this process can be standardized.