> I never saw it spelled like that before. Looks like no one knows how it should be spelled, so all variations are fine. Prior to your comment, I was unaware t

> I never saw it spelled like that before. Looks like no one knows how it should be spelled, so all variations are fine. Prior to your comment, I was unaware that there was any other way to spell it. I very much get the impression that "soup up" is the more common spelling, and (by some measures at least) the more standard. The online version of Merriam-Webster knows of the "soup up" spelling only. https://www.merriam-webster.com/dictionary/soup%20up https://www.merriam-webster.com/dictionary/soup%20up