Feynman's lectures are excellent. One of the best purchases I ever made was the huge printed box set. Just south of $200, but worth every penny when building a deeper understanding of science during my AP classes, then in engineering school. For anyone interested, you can get the boxed set on Amazon for $130 something. If you buy, go through Lew Rockwell, or DP if they have the affiliate link, so a percentage goes back to the liberty movement. I also had a PBS documentary on him called "The Best Mind Since Einstein", which was enlightening but not worth buying. The guy was honest, open and brilliant.
As for government technology...
When they take an existing tech and focus a development project on it for a specific purpose they can get results. You use the case of 3D printers. Early on they did a project to create a print shop which fits in a shipping container. That was so successful they have recently moved on to one that would cost dramatically less than current commercially available printers and would fit in a backpack. These are advances beyond what is available on the shelf, but don't confuse spending millions of dollars to achieve a specific military application with orders of magnitude advances.
To bring it back to the "conspiracy" topic, just look at the thermite found by Jones et all. The aluminum in it was so fine only a few labs in the world had the equipment to make it. More significantly, the carbon based "matrix" which held the oxides and aluminum particles in a perfect blend was only theory, until scientists at Sandia National Labs published papers on the technique a few years after 9/11. Not an Earth shattering advance but a small one meant for specific applications.
The only instances I know of where governments were able to make significant advances were when they took existing theory/practice and built massive research projects around them to produce weapons systems. This worked for the atomic bomb, but by all signs it mostly failed for Star Wars. I know these kinds of projects exist, but one needs to be exceptionally intelligent and well educated to even hope to cut through the hyperbole and speculation. Even then, it takes serious time, usually with little solid evidence in the end.
As someone with a username like yours knows, people will take speculation, or intentionally absurd examples, and run with with them. Most can't evaluate for themselves. People who can do this to some extent should be careful.
"Freedom suppressed and again regained bites with keener fangs than freedom never endangered." -- Cicero