After the post on the shiny rebuilt GE road power, it's only fair to have a look into what Progress Rail has to offer on their side of the table. I'm using the company's recently-changed, formal name of course. For those who are not up-to-date on the current state of North American railroading affairs, Progress Rail is the company (owned by Caterpillar) that purchased EMD a few years ago.
The SD90MAC was arguably the biggest gong show in EMD's recent memory. It happened at a time when they were comfortably resting on their laurels, unaware the fateful changes that were about to occur in the locomotive market in the not-so-distant future (they got beaten badly by GE). What was supposed to be one of the most remarkable locomotives whose presence is to grace the mainlines in modern history, turned out to be an utter disaster (I'll redirect further readings to Wikipedia). As a result, today, the number of SD90s still in operation on a Class 1 Railroad is, if not identically, close enough to zero.
About a couple of years ago (or maybe a little more than that), EMD started making some waves again by claiming to have produced a much more reliable SD70ACe by swapping all the underwhelming Siemens electronics for components from rival Mitsubishi. Perhaps this had inspired the rebuilding of the dismal SD90s, for there was still quite a number of them sitting around idle and waiting to be scrapped. This, I could only speculate. It's an idea Norfolk Southern certainly had warmed to, being at the forefront of this kind of work, even though they didn't have any SD90s on their roster at any time in history. I have no doubt, though, that whoever could offload their SD90s to them, were more than happy to do so.
By Ewwestsr - Own work, CC BY-SA 4.0, Link
So, there you have it, the locomotive that's called the SD70ACu, it's probably what the SD90MAC should have been all along.