This is an outboard power supply, originally made for use in PCs. It does NOT prevent the use of a slot one card. It's a little clungy but it does work. However, It's available only to WAP members. On Three published an excellent magazine that came out for years.
Back issues are no longer available.
WAP has been reprinting some of them, however in its magazine over time. The WAP library and some users still maintain sizeable collections and may be able to help you find the article you're looking for. The author is Stanley M. Miastokowski. WAP is trying to get it placed into the public domain. Kenniston Lord Jr. It discusses Business Basic from a number of perspectives and includes lengthly Basic programs for business users.