Steam-electric is what you'd call an electric motor powered by a steam engine (which isn't what the question is about, but it's still interesting to talk about that). This is based on diesel-electric trains, which are just that but with diesel.
Diesel-electric trains are the norm for diesel trains these days, they indeed run a diesel engine that powers electric motors. They're the norm because they're generally less complex. Primarily you don't have to transmit power mechanically and you don't need a complicated gearbox.
For a modern train, there's also the advantage of being compatible with a fully electric powertrain, and this allows bi-mode (what you'd call hybrid for a car) trains that can run on electricity or diesel relatively easily. Diesel-electric or bi-mode trains are quite useful in area that haven't been electrified.
Steam-electric trains would be an alternative in a world without diesel. And I insist on a "world without diesel" part, because steam was replaced by diesel for a reason: it's a lot more efficient. Not as much as purely electric (there's a reason diesel has been largely replaced by electricity), but certainly more than steam.
You would have steam-electric trains because the rail network isn't completely electrified, and some areas are particular hard to electrify (remote areas, mountains) or just not economic to electrify (low traffic). But wherever you have reliable electrified lines, they would likely be edged out by purely electric or bi-mode trains.
Electric-steam I suppose is what you'd call a steam engine powered by electricity (which is what the question is about).
You could reverse the process to use electricity to boil water for your steam engine. Boiling water with electricity is common in home appliances for cooking or tea. However, doing it to power a steam engine is absurd.
Why? Steam engines aren't very efficient at all. Steam locomotives of yore usually had single-digit energy efficiency, and even modern steam turbines used in power plants today only reach about 40%. Comparatively, a good electric motor will have double that.
You would need absurdly efficient steam engines and absurdly inefficient or inexistant electric motors to justify electric-steam traction over steam-electric or electric traction.
Electric traction + unrelated steam
If electricy is magic and comes without power lines, there's not a good use case for anything but electric traction. If it comes from power lines, steam-electric might make sense for lines without reliable access to electricity.
Any other use case or electric-steam traction would generally be a waste of energy when you could just use the electricity directly.
The only reason to have a steam engine would be if you needed the steam for something else. Maybe you're running a luxury spa-train with steam rooms. I don't know what else you could use steam for (that electricity wouldn't do a better job at) on a train, but that's certainly one use.
Even then, the traction would still be fully electric, and you'd have a separate system that converts electricity into steam.