Feanor, you are probably correct and you have SD-1955+ electronics in an SD-1955 labelled case. From experience, Chinese Quality Assurance leaves a lot to be desired and lots of different versions of the "SD-1955" probably exist with different op-amp configurations and other key components, depending on the actual manufacturer, not necessarily SMSL :-) i.e. the manufacture may be sub-contracted out to other Chinese electronics manufacturers. This probably explains much of the variability in other SD-1955 users listening experiences.

For the benefit of others who might be reading this thread, it would appear that the original SMSL SD-1955 with 24V PSU may still be available direct from some Chinese suppliers as opposed to the newer revisions currently being sold on UK/USA eBay and Amazon:


Smsl Sd-1955 Dir9001 Ad1955 Dac Optical Coaxial Decoder & Power Adapter - Buy Optical Coaxial Decoder & Power Adapter,Digital Audio Decoder,Digital Amplifier Product on Alibaba.com

If nothing else, the internal pictures serve to show that there are considerable differences in the design, layout and components on the circuit boards. Therefore, you might expect them to sound different, because they are.