As with anything bought of any site / or from anyone who is not a PreSonus dealer, you need to make sure it comes with all of the accessories needed to make the product work. That is between you and the seller.
To replace the power supply for the DP88, you will need a 12vdc 3000mA supply.
Contact your PreSonus distributor in Vietnam to purchase one.
Musicland, Co., LTD
319 Dien Bien Phu St, District 3
Ho Chi Minh city, VIETNAM
Tel: (84) 8 39102623
For anyone else reading this and want to find the PreSonus distributor for your country, you can find it on the International Distributors page here: https://www.presonus.com/buy/international-distributors