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).