Comentario sobre Exodo 30:9

לא תעלו עליו YE SHALL NOT OFFER ON IT — on it, i. e. on this altar, but you may offer on the copper altar (cf. Menachot 50b),

YE SHALL NOT BRING UP ‘KTORETH ZARAH’ (STRANGE INCENSE) THEREON — “any incense brought as a freewill offering; for all [offerings of incense] are ‘strange’ to [this altar] except this one [prescribed here].” This is Rashi’s language. But Onkelos rendered ktoreth zarah: ktoreth busmin nuchra’in (“the burning of aromatics which are of strange components,”) and he did not translate it nuchritha “strange incense” [as Rashi interpreted it]. By this translation Onkelos wanted to explain that the sense of the verse is that he should not offer an incense of any other components except those prescribed as He commanded.²⁴⁷This is identical with Ibn Ezra’s interpretation of the verse. Ramban, however, called attention to Onkelos’ text because it required an explanation as mentioned. Similarly, if one were to add to the prescribed composition any other components one would transgress this negative commandment.
Ki Thisa

קטורת זרה,”alien incense.” Rashi understands this to mean that even similar incense offered as a free-willed donation, is considered “alien,” and as such carries a severe penalty. Onkelos translates the verse as referring to spices not listed in Parshat Ki Tissa that begins forthwith. The prohibition of changes in the composition of the spices includes even adding an additional spice to the ones the Torah authorized and whose proportions the Torah specified. (30,22-38)