diff --git a/rdflib/plugin.py b/rdflib/plugin.py
index 23699e68d..556b78804 100644
--- a/rdflib/plugin.py
+++ b/rdflib/plugin.py
@@ -579,18 +579,6 @@ def plugins(
     "rdflib.plugins.sparql.results.xmlresults",
     "XMLResultParser",
 )
-register(
-    "application/sparql-results+xml; charset=UTF-8",
-    ResultParser,
-    "rdflib.plugins.sparql.results.xmlresults",
-    "XMLResultParser",
-)
-register(
-    "application/rdf+xml",
-    ResultParser,
-    "rdflib.plugins.sparql.results.graph",
-    "GraphResultParser",
-)
 register(
     "json",
     ResultParser,
@@ -627,3 +615,14 @@ def plugins(
     "rdflib.plugins.sparql.results.tsvresults",
     "TSVResultParser",
 )
+
+graph_parsers = {parser.name for parser in plugins(kind=Parser)}
+result_parsers = {parser.name for parser in plugins(kind=ResultParser)}
+graph_result_parsers = graph_parsers - result_parsers
+for parser_name in graph_result_parsers:
+    register(
+        parser_name,
+        ResultParser,
+        "rdflib.plugins.sparql.results.graph",
+        "GraphResultParser",
+    )
diff --git a/rdflib/plugins/stores/sparqlconnector.py b/rdflib/plugins/stores/sparqlconnector.py
index e2bb83909..529355567 100644
--- a/rdflib/plugins/stores/sparqlconnector.py
+++ b/rdflib/plugins/stores/sparqlconnector.py
@@ -9,8 +9,10 @@
 from urllib.parse import urlencode
 from urllib.request import Request, urlopen
 
-from rdflib.query import Result
+from rdflib.plugin import plugins
+from rdflib.query import Result, ResultParser
 from rdflib.term import BNode
+from rdflib.util import FORMAT_MIMETYPE_MAP, RESPONSE_TABLE_FORMAT_MIMETYPE_MAP
 
 log = logging.getLogger(__name__)
 
@@ -22,16 +24,6 @@ class SPARQLConnectorException(Exception):  # noqa: N818
     pass
 
 
-# TODO: Pull in these from the result implementation plugins?
-_response_mime_types = {
-    "xml": "application/sparql-results+xml, application/rdf+xml",
-    "json": "application/sparql-results+json",
-    "csv": "text/csv",
-    "tsv": "text/tab-separated-values",
-    "application/rdf+xml": "application/rdf+xml",
-}
-
-
 class SPARQLConnector:
     """
     this class deals with nitty gritty details of talking to a SPARQL server
@@ -41,7 +33,7 @@ def __init__(
         self,
         query_endpoint: Optional[str] = None,
         update_endpoint: Optional[str] = None,
-        returnFormat: str = "xml",  # noqa: N803
+        returnFormat: Optional[str] = None,  # noqa: N803
         method: te.Literal["GET", "POST", "POST_FORM"] = "GET",
         auth: Optional[Tuple[str, str]] = None,
         **kwargs,
@@ -95,7 +87,7 @@ def query(
         if default_graph is not None and type(default_graph) is not BNode:
             params["default-graph-uri"] = default_graph
 
-        headers = {"Accept": _response_mime_types[self.returnFormat]}
+        headers = {"Accept": self.response_mime_types()}
 
         args = copy.deepcopy(self.kwargs)
 
@@ -170,7 +162,7 @@ def update(
             params["using-named-graph-uri"] = named_graph
 
         headers = {
-            "Accept": _response_mime_types[self.returnFormat],
+            "Accept": self.response_mime_types(),
             "Content-Type": "application/sparql-update; charset=UTF-8",
         }
 
@@ -188,5 +180,27 @@ def update(
             )
         )
 
+    def response_mime_types(self) -> str:
+        """Construct a HTTP-Header Accept field to reflect the supported mime types.
+
+        If the return_format parameter is set, the mime types are restricted to these accordingly.
+        """
+        sparql_format_mimetype_map = {
+            k: FORMAT_MIMETYPE_MAP.get(k, [])
+            + RESPONSE_TABLE_FORMAT_MIMETYPE_MAP.get(k, [])
+            for k in list(FORMAT_MIMETYPE_MAP.keys())
+            + list(RESPONSE_TABLE_FORMAT_MIMETYPE_MAP.keys())
+        }
+
+        supported_formats = set()
+        for plugin in plugins(name=self.returnFormat, kind=ResultParser):
+            if "/" not in plugin.name:
+                supported_formats.update(
+                    sparql_format_mimetype_map.get(plugin.name, [])
+                )
+            else:
+                supported_formats.add(plugin.name)
+        return ", ".join(supported_formats)
+
 
 __all__ = ["SPARQLConnector", "SPARQLConnectorException"]
diff --git a/rdflib/plugins/stores/sparqlstore.py b/rdflib/plugins/stores/sparqlstore.py
index f9827cf94..7f66366cb 100644
--- a/rdflib/plugins/stores/sparqlstore.py
+++ b/rdflib/plugins/stores/sparqlstore.py
@@ -128,7 +128,7 @@ def __init__(
         sparql11: bool = True,
         context_aware: bool = True,
         node_to_sparql: _NodeToSparql = _node_to_sparql,
-        returnFormat: str = "xml",  # noqa: N803
+        returnFormat: Optional[str] = None,  # noqa: N803
         auth: Optional[Tuple[str, str]] = None,
         **sparqlconnector_kwargs,
     ):
diff --git a/rdflib/util.py b/rdflib/util.py
index ab594b5be..96260fc20 100644
--- a/rdflib/util.py
+++ b/rdflib/util.py
@@ -74,6 +74,47 @@
 _AnyT = TypeVar("_AnyT")
 
 
+SUFFIX_FORMAT_MAP = {
+    "xml": "xml",
+    "rdf": "xml",
+    "owl": "xml",
+    "n3": "n3",
+    "ttl": "turtle",
+    "nt": "nt",
+    "trix": "trix",
+    "xhtml": "rdfa",
+    "html": "rdfa",
+    "svg": "rdfa",
+    "nq": "nquads",
+    "nquads": "nquads",
+    "trig": "trig",
+    "json": "json-ld",
+    "jsonld": "json-ld",
+    "json-ld": "json-ld",
+}
+
+
+FORMAT_MIMETYPE_MAP = {
+    "xml": ["application/rdf+xml"],
+    "n3": ["text/n3"],
+    "turtle": ["text/turtle"],
+    "nt": ["application/n-triples"],
+    "trix": ["application/trix"],
+    "rdfa": ["text/html", "application/xhtml+xml"],
+    "nquads": ["application/n-quads"],
+    "trig": ["application/trig"],
+    "json-ld": ["application/ld+json"],
+}
+
+
+RESPONSE_TABLE_FORMAT_MIMETYPE_MAP = {
+    "xml": ["application/sparql-results+xml"],
+    "json": ["application/sparql-results+json"],
+    "csv": ["text/csv"],
+    "tsv": ["text/tab-separated-values"],
+}
+
+
 def list2set(seq: Iterable[_HashableT]) -> List[_HashableT]:
     """
     Return a new list without duplicates.
@@ -331,26 +372,6 @@ def parse_date_time(val: str) -> int:
     return t
 
 
-SUFFIX_FORMAT_MAP = {
-    "xml": "xml",
-    "rdf": "xml",
-    "owl": "xml",
-    "n3": "n3",
-    "ttl": "turtle",
-    "nt": "nt",
-    "trix": "trix",
-    "xhtml": "rdfa",
-    "html": "rdfa",
-    "svg": "rdfa",
-    "nq": "nquads",
-    "nquads": "nquads",
-    "trig": "trig",
-    "json": "json-ld",
-    "jsonld": "json-ld",
-    "json-ld": "json-ld",
-}
-
-
 def guess_format(fpath: str, fmap: Optional[Dict[str, str]] = None) -> Optional[str]:
     """
     Guess RDF serialization based on file suffix. Uses