How are those connectors called? (see images)
It is a widely-used 4-pin female connector, a crimp housing with four female crimp terminals inserted.  There are many manufacturers that make a connector like this, but Molex makes one Part Number: 50-57-9004 (SL™ Crimp Housing, Single Row, Version A, Non-polarized, 4 Circuits) in the SL Modular connector line.  You can order this housing on Digi-Key.

You can easily crimp these terminals yourself with a low cost hand crimping tool if you want to make cable assemblies with this kind of connector.  You'd need to buy a bag of female crimp terminals to use, then after crimping the wires, you insert the terminals into place in the housing.