Noting the desire to support both 240 and 250 V, I offer the assembled audiophile's possibly the most versatile transformer configuration I've seen, from the Rotel 850 Power Amplifier. This has full dual-mono construction. Each transformer has 2 separate 120V primaries, with a 10V centre tap. This allows each primary to be 110V or 120V (and usefully run in parallel), and (when joined in series), 220V, 230V, or 240V.
No 250V, sorry!
850_tran by plybench, on Flickr
BugBear
No 250V, sorry!
850_tran by plybench, on Flickr
BugBear