confused about 20 amp power cables

I've recently acquired a pre-owned T+A PA 3100 HV integrated and this is my first exposure to a 20 amp power cable. The supplied cable has what I think is a C19 IEC connector (20 A) on the amp end, but the connector on the wall side has parallel hot and neutral blades as opposed to the 20 amp T blades. Is that end really rated at 20A? 

I have a dedicated 110V 20 amp circuit with 20 A receptacles, but is about 10 ft from my equipment. I am currently plugging the amp's supplied cable into an Oyaide OCB-1 SX V2 power conditioner which is plugged into the 20A wall receptical. The wall plug on the Oyaide appears to be a 15A plug and the  4 distributed receptacles are not 20A  and I assume they are rated for 15A. Is this dangerous to have this 15A section between wall and amp?

Would I be better off, or safer to find a 20A extension cable so I could plug the amp directly into the wall?  I've recently started building my own PCs and could make a 10 ft one with C19 on one end and 20A wall plug on the wall side ( ouch for wire cost for 10ft).  I know that its unlikely the amp will ever draw more than 15A. 

Any suggestions would be helpful!