A case can be made for each theory suggested by TRomano and FumbleFingers, but given the context and the historical period referenced, ram-charged is probably an automotive metaphor.
A search through Google Books Ngrams shows many instances of computers being RAM-charged. This is an extension of charge, in this sense given by Macmillan:
to put electricity into a piece of electrical equipment such as a battery
That is, the computer is like a typewriter which has been energized or activated with RAM, which in computing refers to random-access memory, the "working memory" a computer uses to perform its calculations.
But I do not think this is the meaning the author intended. For one, the story being related is one of the author's ignorance of computers when they were first introduced to him in high school in 1970. He also writes of the primitiveness of the machine I/O in simplistic words, describing typewriter gadgets and a little golf ball and green bar paper. It would be incongruous to use a technical term, still used in the modern day, to relate such a story. Moreover, this book is a programming book which mentions RAM meaning random-access memory in many places. RAM is almost always printed in all-caps, whereas here it is lowercase, suggesting that ram does not mean RAM.
What might also have interested a teenaged American boy in 1970— this being the height of the muscle car era— is the ram charge effect in an internal combustion engine. To greatly simplify, the idea was that a large, long air intake would cause air to be compressed and forcefully pushed (i.e. rammed) into the engine, in turn leading to more air being fed into the cylinder, in turn boosting power.
The prominent air intakes on cars like this 1969 Dodge Super Bee are supposed to maximize this effect (although on some cars, its main effect was merely to look more powerful).
Thus, something that was ram-charged was something whose power or speed has been boosted above normal. The computers which the author encountered, to his young mind, seemed like nothing more than fast typewriters.
This term was never especially common (ram charge effect does not appear once in Google Ngrams from that era), and nowadays, I would only expect it to be familiar with motorsports enthusiasts. In cars, the turbocharger and supercharger were more effective and found wider usage, so the average person would probably understand turbocharged or supercharged better than ram-charged. In fact, I suspect many people use those terms without even being aware that they originated in automotive engineering, and refer to different devices.
As FumbleFingers notes, some other colloquial ways to describe something as an artificially boosted version of X are to call it a turbo X or turbocharged X, or to say it is X on steroids.