Old style hardware upsampling with built in IC never did much for me. It might have sounded "smoother" but also stuffy and dead or boring. The life and edge were reduced.
But the recent advent of excellent low jitter hirez DACs and cheap and powerful music computers spawned the emergence of great software for interpolative upsampling, or "resampling." The steppy waveform of 44.1kHz is redrawn into a smooth analog like waveform, using advanced algorithms to fill in the missing music between the input digital samples.
SoX is one resampling algorithm that I've used, it comes included with Moode Audio software for Raspberry Pi. Sounds excellent when resampling from 16/44.1kHz to 32/384kHz. Slightly soft, but most people like that. The algorithm settings are not easily adjustable in Moode.
Even better sounding is
Roon upsampling DSP, running on Windows PC, outputting to SoTM network audio adapter thingy. This sounds really good, smooth and musical, but clearer than Sox with Moode settings. Upsampling settings in Rune aren't much adjustable either.
Another I want to try is
HQPlayer software on the PC, which also outputs to the NAA. Supposed to be even better than Roon, much more adjustable algorithm settings. Tweakers delight.
As Mike said, these new high end resampling algorithms can interpolate 44.1kHz input to any high rez sampling speed, even DSD512, which is like 5GHz? Resample to whatever is the highest native resolution of your DAC, so you can eliminating the lesser SQ onboard upsampler in the DAC IC or separate upsampling IC before the DAC in older units.