There are 2 main sources of acetyl-CoA:
Glucose: At the end of glycolysis, the PDC converts pyruvate to acetyl-CoA.
Fatty acids: β-oxidation of fatty acids yields acetyl-CoA. Note that β-oxidation of some fatty acids produces propionyl-CoA, which is converted to succinyl-CoA. Succinyl-CoA can enter the citric acid cycle as an intermediate.