Good Morning Turtle64,
Reichelt’s information is correct in principle. You would need little modifications to use the StromPi 2 with the Raspberry Pi 3b+.
left: StromPi2, middle: Raspberry Pi 3b+, right: Raspberry Pi 3b
The Problem is caused by the low profile design in combination with the POE pins. As you can see on the photo above, the pad, where the marked pogopin would connect to, are shited inwards at the Raspberry Pi 3b+.
This causes the pin collision shown in the picture above.
But with a GPIO extension (shown below) it would be possible. Just the reset connection has to be connected manually (e. g. by soldering).
Now I got a Strompi2 and a Raspi 3B+.
The problem is that the reset pin for Raspi3 on the bottom of the Strompi2 collides with the POE connector on the Raspi 3B+.
In my application I do not need the reset pin, so I just cut it away. Now it works fine.