Wondering about SP20:
Inside SP20 box are two PCB, is there possibility for have only one core plate running? by connecting psu to only one them?
I believe so. I had to RMA one of the first SP20's due to the board sliding loose during shipping. One of the boards had a cracked VRM. I tested the other board by itself - unplugged the "bad" board completely. It worked just fine, of course at half the hash speed.
Not condoning doing so, just my experience with running one board.