In 1998, dCS invented the terms “Upsampling” and “Upsampler” to define a separate digital-to-digital converter unit used to convert low-resolution digital data to a higher resolution, higher sample rate data stream, to present a high-resolution DAC with better data and so replace part of the DAC’s oversampling function.
An Upsampler appears to make it easier for the DAC to carry out the conversion to analogue by taking over part of the processing load.
The two terms have been misused by many other manufacturers that have missed the point about the “separate unit”. An “upsampling DAC” is a contradiction.