Logically, you want to treat your components starting with the first link in the signal chain. Assuming power cords remedy some deficiency in the power the component is receiving, by the time the signal reaches the amp the "damage" is done.
Not necessarily. "The damage" introduced by each component is a matter of degree. Your logic ignores the possibility that the magnitude of the damage that will be introduced by the first link in the chain (in the absence of the better pc), as amplified by what follows, might be less, or even much less, than the damage that may be introduced by a component which is later in the chain (in the absence of the better pc).
See my post earlier in this thread, and the other thread I linked to, for some specific reasons why that possibility may occur. And why, in fact, lack of good shielding on the amp's pc may RESULT in problems being introduced earlier in the chain.
Regards,
-- Al