In this blog Lead Field Conversion Mapping written almost 4 years ago, we shared about standard fields mapping when a lead is converted to Account, Contact, and Opportunity.
By default, Lead Source is not mapped to Account Source, only to Contact and Opportunity, and you can't just simply configure the field mapping. You can follow this article by creating custom fields, configure the lead fields mapping, and workflow.
With this free managed package app "Lead Source Mapper" by CRM SuperStars, admin just needs to install the app, no extra fields and etc. need to be configured. When a lead is converted to new Account, the Account Source will be auto populated from Lead Source. If you convert the lead to existing Account and Account Source have value, it will not change. But if the existing Account Source is blank, the new value from Lead will update the Account Source.
Type: Managed Package; AppExchange
Publisher: CRM SuperStars
Blog last updated: 17 August 2017