This translation is completely off. Based on my understanding of ủng hộ from various Vietnamese teachers and friends in Vietnam, it means support in a moral sense. As in cheering someone on or comforting them. Not physical support. In which case "a simple support" is wrong. I suppose it could be the equivalent of "I need some simple support." But it can't be "a" since moral support isn't a countable noun. You can't have two simple (moral) support. But you can have some simple (moral) support.
The English sentence only has one possible meaning. For example: "I need a simple support to keep the broken table from collapsing." In other words, "a" is appropriate only if "support" refers to a physical object. If "simple support" refers to somebody giving me help, defending me, or arguing in my favor, then the sentence should be "I need simple support." or probably "I need some simple support." Using "a" with this meaning is wrong.