On the other hand, he did not accept as well founded the charge made by some of his critics that while he was a good observer, he had nopower of reasoning.

谓语动词的结构是：accept + 宾语 as + 过去分词。

其中，as well founded 是宾语补足语。as 看作介词即可，不需要过多分析。well founded 是过去分词作 as 的宾语。

【特别提示】因本句 accept 的宾语过长而后置（the charge 是其宾语，但后面跟了一个作定语的过去分词短语和 that 引导的同位语从句），所以把宾补as well founded 提到宾语之前。