DC loads are generally expressed in:

In DC power systems - such as -48V DC telecom plants - the bus voltage is held constant by the rectifier and battery, so the ampere draw directly and completely represents the load demand. Expressing loads in amperes allows engineers to size conductors, fuses, and battery capacity without power factor considerations, which do not exist in DC circuits.

Volts is a unit of electrical potential, not a measure of load or energy consumption, and cannot represent how much current or power equipment demands.

Volt-amperes (VA) is the unit for AC apparent power and accounts for the phase difference between voltage and current in AC circuits; DC circuits have no reactive component, making VA inapplicable.

Watts can describe DC power mathematically, but industry convention for DC power system design - especially in telecom - uses amperes to size circuits at a known fixed voltage rather than watts.