I think that's what it is. On CPC Wiki I found some discussions about PCW9256 - there is power on the odd pins, i.e. on the + 5V part, on the GND part, but for me all the odd ones are connected together and to GND. Additionally, there is a separate power plug. Thanks for this remark about the changed power supply, because out of laziness I could not check where the voltage is going
I will ask right away: where can I find any floppy disk images, because a cursory search shows that PVC was probably not very popular computers.