Received this Plus/4 today from eBay. Sold as untested with no PSU and fully expected this to be broken.
The power supply connector is a 4 pin affair that looks similar to the C128 and Amiga but it is not. All is not lost however as if you remove the original connector it can be directly replaced with one from a C64, and that’s just what I did.
The swap was a very quick operation and to my surprise the system fired up with no issues other than some keys on the keyboard need a little more force than others.
I think the SD2IEC is also compatible but I will need an external power supply for it as mine normally plugs into the cassette port of a C64/128 for its power needs.