É possível, mas não recomendado. . Do FAQ da Embaixada dos EUA em Cingapura, nº 5:
Q.5 If I am a third-country national living in the Singapore, can I apply for a nonimmigrant visa in the Singapore? [sic]
Applicants are generally advised to apply in their country of nationality or residence. Any person who is legally present in the Singapore may apply for a visa in the Singapore . However, applicants should decide where to apply based on more than just convenience or delay in getting an appointment in their home district. One thing to consider, for example, is in which consular district the applicant can demonstrate the strongest ties.