My first thought is manufacturers of PC’s prefer to keep their performance data proprietary as much as they can. Why give their competitors easy access to performance data or also, it becomes a specification contest with no connection to sonic performance.
I worked in Automotive where our products had to meet EMI/RFI emissions per the SAE and DIN specs. I do not recall specifications or standards for devices that attenuate EMI/RFI. Maybe I am wrong but that leaves noise conditioner designers to find their best design paths to meet performance or audio goals. But without measurement or industry performance standards the claims and measurements of Power Conditioners with respect to we consumers could become very confusing. It is already confusing for us because results vary between applications, local EMI noise conditions and how our unique audio systems respond to PCs.