If the Cambodian passport holders want to apply visa at Vietnam Embassy, they should to know that:
Visa administrative Institution: Vietnam Embassy
Processing time: depends on you how fast you need. But for sure, you should make a call to Vietnam Embassy for details.
Required Documents: passport, money and 1 new envelope with stamp on it and your exact home address in order to avoid losing issues.
How to apply: please take a look at contact information of Vietnam Embassy below
EMBASSY OF VIETNAM IN PHNOM PENH, CAMBODIA
Address: 436 Monivong Blvd., Khan Chamcarmon, Phnom Penh
Phone: (855) 23 726 273/ 726 274
Email: firstname.lastname@example.org | email@example.com
CONSULATE GENERAL OF VIETNAM IN SIHANOUK VILLE, CAMBODIA
Address: 310, Ekareach Street, Mittapheap District, Sihanouk Province
Fax: (855) 3493 3669
CONSULATE GENERAL OF VIETNAM IN BATAMBANG, CAMBODIA
Address: Road No.3, Batambang province, CAMBODIA