Thanks to my wife Beverly ... I got an early Christmas present ... we sent off for an adapter for my 7800 ProSystem, and I powered it up for the first time in 30 years tonight:
It all works perfectly! Can't wait to start using it to develop my Sky Scraper game, and also add it to my music studio! One thing: You have to keep the console absolutely still, or it will glitch. May need to be opened up, and the dust of 30 years blown out of the cartridge port.