Can I use an adjustable DC power supply to discharge a battery?
No you generally cannot. Otherwise there would be no need for &quot;Electronic Loads&quot;.

These devices can be set to constant current, constant resistance or constant power draw to emulate whatever your real load is.
They are available from a number of sources, generally cost will increase with increasing power capability (and with the accuracy and pedigree of the maker). Usually you can use them with suitable interfaces to plot battery discharge curves, examine response to pulsed loads and that sort of thing.