You need a regulated switchmode 12V 2A adapter with centre pin positive.
Identifying Maxtor External Storage Power Supplies :http://seagate.custkb.com/seagate/crm/selfservice/search.jsp?DocId=186849http://support.seagate.com/kbimg/2087-9.jpg
Try Sim Lim Square or Sim Lim Tower. Otherwise try the Jalan Besar Plaza on Kitchener Rd. That's where I used to buy my spare parts 20 years ago.