Taken from post_format_meta_box
;
if ( current_theme_supports( 'post-formats' ) ) {
$post_formats = get_theme_support( 'post-formats' );
if ( is_array( $post_formats[0] ) ) {
print_r( $post_formats[0] );
// Array( supported_format_1, supported_format_2 ... )
}
}