Hi
Different adapter behaves differently - not all performs XML conversion. For HTTP sender adapter, it extracts the HTTP request to the main payload and attachments. It does not convert the content automatically to XML. You can check out what is available for the HTTP adapter in the links below.
Configuring the Java HTTP Adapter on the Sender Channel - Advanced Adapter Engine - SAP Library
HTTP Requests Supported by the Java HTTP Adapter - Advanced Adapter Engine - SAP Library
Rgds
Eng Swee