IMO, popular opinion has it backwards, if your equipment is well designed and in good condition, the engineers will have built in significant power conditioning betwixt your incoming ac line & the dc buss immediatly downstream, power cord & other minute effects to incoming voltage will be minimal. If you have old equipment with worn out capacitors ,or the designer skimped on conditioning, you may hear more of a difference. If you are on good terms with a local repair shop, it is very easy to hook up an osciloscope to the dc buss in your equipment and detect any differences. There is no magic to this one, if you can't see a change in dc voltage level on a scope, your equipment can't see it either.
cable upgrades , real or rip off
im sure this has been done to death on other threads, but im somewhat new to the high end audio thing. but i must ask do these items make a huge diff. , a small one or something in between. i cant help but asking myself why when a company is trying to produce a knockout item such as a intgrated amp that costs say 3000.00 would they skimp on something like a 300.00 powercord if it would make there product sound that much better?