I'm using the TSaveTextFileDialog component in Delphi XE3, but when a VCL Style is enabled, the encoding combobox is drawn using the current VCL style.

How can I fix this, I mean disable the VCL style for the combobox?

The parent class (TOpenTextFileDialog) of the TSaveTextFileDialog component adds a set of Vcl components to implement the Encodings and EncodingIndex properties, you can disable the Vcl styles on these Vcl controls using the StyleElements property. unfortunately these components are private so you need a little hack in order to gain access and disable the Vcl Styles.

Here you have two options.

Using a class helper.

You can introduce a helper function to get the Panel component which contains the Vcl controls of the dialog.

type
 TOpenTextFileDialogHelper=class helper for TOpenTextFileDialog
  function GetPanel : TPanel;
 end;

function TOpenTextFileDialogHelper.GetPanel: TPanel;
begin
  Result:=Self.FPanel;
end;

then you can write a method to disable the Vcl Styles, like so :

procedure DisableVclStyles(const Control : TControl);
var
  i : Integer;
begin
  if Control=nil then
    Exit;
   Control.StyleElements:=[];

  if Control is TWinControl then
    for i := 0 to TWinControl(Control).ControlCount-1 do
      DisableVclStyles(TWinControl(Control).Controls[i]);
end;

And finally use on this way

  DisableVclStyles(SaveTextFileDialog1.GetPanel);
  SaveTextFileDialog1.Execute;

RTTI

Another option is use the RTTI to access the private Vcl components.

var
  LRttiContext : TRttiContext;
  LRttiField :TRttiField;
begin
  LRttiContext:=TRttiContext.Create;
  for LRttiField in LRttiContext.GetType(SaveTextFileDialog1.ClassType).GetFields do
   if LRttiField.FieldType.IsInstance and LRttiField.FieldType.AsInstance.MetaclassType.ClassNameIs('TPanel') then
    DisableVclStyles(TPanel(LRttiField.GetValue(SaveTextFileDialog1).AsObject));

  SaveTextFileDialog1.Execute;
end;