No matter how word-for-word a translation tries to be, there will always be some confusing sentence that requires interpretation. Sometimes, the more word-for-word translations just leave it confusing, but other times even the NASB and ESV (for example) feel the need to interpret.
Rom 5:9 says, “Much more then, having now been justified by His blood, we shall be saved from the wrath of God through Him” (NASB). The italics show that “of God” is not in the Greek, which reads, σωθησόμεθα δι᾿ αὐτοῦ ἀπὸ τῆς ὀργῆς.
The ESV simply says “the wrath of God” and footnotes 1 Thess 1:10 and 2:16, referencing also Romans 1:18. Cranfield adds the reference to 1 Thess 5:9.
HCSB and KJV simply say, “from wrath.” Others say “God’s wrath” (NIV, NRSV), and the NET adds the footnote, “Grk, “the wrath,” referring to God’s wrath as v. 10 shows.” NLT has “God’s condemnation.” While v 10 does not mention “God’s wrath,” the connection between vv. 9 and 10 is certainly there.
Interestingly, none of these parallels say it is “God’s” wrath. 1 Thess 1:10 says, “Jesus, our deliverer from the coming wrath” (Ἰησοῦν τὸν ῥυόμενον ἡμᾶς ἐκ τῆς ὀργῆς τῆς ἐρχομένης). 1 Thess 2:16 has, “wrath has caught up with them at last” (ἔφθασεν δὲ ἐπ᾿ αὐτοὺς ἡ ὀργὴ εἰς τέλος). 1 Thess 5:9 reads, “For God has not appointed us for wrath, but to obtain salvation through our Lord Jesus Christ” (οὐκ ἔθετο ἡμᾶς ὁ θεὸς εἰς ὀργὴν). Always have to check cross references to see if they actually support the proposition.
Personally, I see no reason to add “of God” since none of the parallels actually say it. Paul didn’t feel the need, and to my ears it changes the message a little. Of course it is God’s wrath, but the emphasis is not on the cause of the wrath but on the event itself.