The English lyrics for the hymn "I Sing the Mighty Power of God" were written and translated by Isaac Watts (1674-1748). He was an English minister and prolific hymn writer whose hymns include "Our God, Our Help in Ages Past" & "Joy to the World". The tune commonly used for the hymn is similar to one first published in Germany in the Gesangbuch der Herzogl (Duke's Hymnbook) for the Church called Wirtembergischen katholischen Hofkapelle. The melody was significantly altered and adapted (ref. https://www.hymnologyarchive.com/hosanna-loud-hosanna) over the years for different hymns in various German and English hymnbooks, including a version by the composer William H. Monk. Monk wrote music for "Abide with Me" and "All Things Bright and Beautiful" and many other hymns, and was the original editor of the Church of England collection known as "Hymns Ancient and Modern", first published in 1861. It may have been this or another English Hymnbook which gave the tune the title "Ellacombe", since this is the name of a district of Torquay in Devon.
Piano sheet music, midi and mp3 files for this hymn can be downloaded using the links in the left-hand menu, or see below.
Here is a video of I Sing the Mighty Power of God (Tune: Ellacombe):
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The image below is the first page of the sheet music, and here you can download the full sheet music for I Sing the Mighty Power of God (Tune: Ellacombe) in PDF format.