Jeter, not Powers, and The Anubis Gates is not particularly steampunky, especially compared to Powers' friend James Blaylock's works.
Ao ot was, but The Anubis Gates was still one of the works originally indicated:
"...the term steampunk originated largely in the 1980s[27] as a tongue-in-cheek variant of cyberpunk. It was coined by science fiction author K. W. Jeter,[28] who was trying to find a general term for works by Tim Powers (The Anubis Gates, 1983), James Blaylock (Homunculus, 1986), and himself (Morlock Night, 1979, and Infernal Devices, 1987) — all of which took place in a 19th-century (usually Victorian) setting and imitated conventions of such actual Victorian speculative fiction as H. G. Wells' The Time Machine."
All works mentioned there ought to go on a Steampunk Appendix N.