The stock wallwart SMPS packed with the Adi-2 and Adi-2 Pro (and other RME units) is somewhat substandard, and RME knows this.
While the output voltage itself is not the problem (it *is* spikey and ripple-laden, but the internal PSU concept of those interfaces handles this with no problem), the mains leakage current is as bad as it gets, it's a bog-standard lowest-cost SMPS with 1nF or so of "EMC"-capacitance from secondary to primary (and the primary is rectified mains, hence the current isn't a benign 50Hz-only sinusoid).
The resulting balancing current which return via PE/mains of the connected components (amp, source/PC) can induce considerable noise when lesser quality RCA cables are used, notably longer ones. Voltage drop along the shield, both R*i and L*di/dt components. A systems EMC/SigInt issue, of course, the interfaces themselves are perfectly fine. A low leakage medical grade, well-filtered SMPS would be in order to solve this. I personally break the current loop by inserting a 12V/12V medical D/DC-converter with only 20pF coupling capacitance, balancing current went down 30dB easily.
The second issue with the stock supply is that it is mechanically fragile, the DC cable and its strain relief is not durable at all and will fail quickly when used/moved a lot. In a permanent home or studio install this is acceptable but it is certainly not the level of industrial quality that I would like to see here, compromising those otherwise very well-made and rugged products.