Invalid date/time: 2019-04-29T00:00:00-07:00

Date d = System.today();
Datetime myDT = datetime.newInstance(d.year(), d.month(),d.day());
String myDate = myDT.format('yyyy-MM-dd'T'HH:mm:ssXXX');
Datetime dd = DateTime.valueof(myDate);
System.debug('ddddddddddd'+dd);