I use a power conditioner more for the surge protection and I thought using my ancient $100 monster PLC was doing the HP an injustice. In keeping with the "value" theme, a now discontinued PS Audio powerplay unit is used.I guess the unit is doing its job as I can instantly hear a difference in overall dynamics compared to the monster. As a bonus, it looks much nicer in the rack than the mess of cable on the floor.
The power cord definetly is a YMMV thing. There doesn't seem to be a consistent thread with entry level cords(the only level I'm willing to try).I've had great results with the dubious Mapleshade cord, but it isn't a permanent fixture for obvious reasons. For now I use the Signal Cablle "magic" cord. While many users of this cord report good results, I don't hear any noticeable improvement over the stock cord. Fortunately, it's inexpensive. If I come across an exceptional deal, I may splurge for a Nordost or a Shunyata.
The cable thing really is a roll of the dice. I do believe starting with decent wall AC feeding the system and protection should be addresed.