Ever since Enerwave stopped manufacturing its 20A Z wave outlet, The only US option for controlling devices with a load higher than 15 A was one of the high load micros, which didn’t fit easily in the wall and often cost more than $150 per outlet.
ConnectSense has just come out with a new energy monitoring in wall outlet with two independently controlled sockets that should fit in place of the existing 20 amp outlet. These are intended for use with HomeKit, but also have an Alexa integration. So you can get to smartthings through one of those two routes depending on exactly how you have your system set up. (For HomeKit integration, you need to be running homebridge, so unless you are already doing that, you will probably prefer the echo integration.)
I haven’t seen the specific device personally, but I have some of the company’s other devices and find them to be very well engineered. This model is UL listed. 
List price on this is $99.95, but remember that you are getting two independently controlled sockets for that cost. And with potentially an easier install than the micros.
(The $79.99 Price is for the 15 amp model. The 20A lists at $99.99.)
So I think it will be worth looking at for quite a few people.
FAQ: Can I trigger an Echo Action without Speaking to It?
(Currant, Who have a smartthings integration for their plug-in pocket socket, have said that they are working on an in wall outlet that will support 20 A and would probably have smartthings integration as well, but it’s not yet available for sale and there’s no announced timeline.
So if you want better integration, you could wait for that one, but who knows when it will arrive. 
