The power dissipation in any class A amplifier is constant, whether Quiescent or at Full power. So the power draw from the mains is constant.
Class D is different. Power is drawn at the transition of the digital switching, and these is often back noise at 50-100Khz from switchmode PSU's as well.
This can get back into the mains chain and by radiation into the audio chain, if attention is not paid to the routing of the cables (mains cable at 90 degrees to signal cables). This is where a screened mains cable comes into its own, in reducing the potential noise floor. However, a proper mains filter, and, if you have smps, screened mains lead. Will make a much bigger difference than ANY expensive boutique mains cable, and is substantially cheaper. Think a quarter of the price of a Russ Andrews BS mains block.
These
IEC C14 to C5 Adaptors are available at a much better price, just add shipping (also available from RS and PartsExpress, etc.).