For whatever reason, sometimes I am only able to find one card of certain players. To be considered a One-Card Wonder, a player must have been active since 1991 (when I started paying attention).
This is another one that I cannot provide a scan for, but it's a 1997 Pacific Crown Collection card. It looks like he may have one or two other Red Sox cards that I have simply been unable to find, but this is the only one I own at this point.
Delgado only made the Majors in 1996. He appeared in 26 games, mostly as a late-inning defensive replacement, appearing at catcher, left field, third base, right field, first base, and second base. He had only 24 at-bats in 1996 and hit .250/.348/.250/.598 with no extra base hits. Delgado bounced from organization to organization after 1996, never again reaching the Majors.
EDIT: I recently added a 1996 Ultra card. Alex Delgado is no longer a one-card wonder.