Every inline contact junction affects DTCD (dynamic transient current delivery) which is a major factor in power cord and power conditioner performance. We go to incredible (obsessive compulsive) lengths to maximize DTCD performance. We manufacturer our own wire and connectors. The outlets have contacts that are made from solid copper - not brass or bronze. Use use cryogenically treated IEC inlets. We even make our own custom wiring terminals inside the DENALI. Our Alpha and Sigma power cords are made with our own connectors that are constructed of solid copper base metals. So any adapter that you may use inline will be detrimental to the performance.
However, there are practical concerns when doing a trial of one of the power conditioners. Some people have their own expensive power cord and want to use it. Fine, we understand - just understand that if you use an adapter, you are not getting the full potential of the power conditioner. You can use an adapter for a trial but we do not recommend it for long term use of the power conditioner.
There are other more practical concerns about adapters. We make adapters to convert C15 to C19 and C19 to C15 and they are very high quality. However, just by the nature of IEC inlets and connectors - they are just not that great for contact integrity. It is far too easy for the connector to become loose or perhaps it was not fully inserted. If a contact is not fully engaged, the components will work OK but there will be a build up of heat at the contact junctions. This thermal noise can affect the sonic performance and in some cases can become a hazard.
Entertainment systems have high powered amplifiers and multiple components which means that a typical system can pull as much current as a space heater. We use FLIR and thermal probes in the development of our products and you would be surprised how hot a properly functioning connector can become when under a typical load.
If you want to use an adapter to a single component - I don't have a huge problem with it even though it will degrade potential performance compared to a direct connection with a high performance power cord. However, I DO NOT recommend using any adapter between the power cord and a high capacity power distributor or conditioner.