Ive heard it earlier from a electrician and a teacher, but I seem to keep forgetting it. So to start remorizing it I started to write this article. Its actualy pretty easy when you remember why it is called VDD or VCC for power and VSS and VEE for ground.
Because of the Transistors inside the IC your connecting it to. ill qoute: "Apparently this terminology originated in some way from the terminals of each type of transistor, and their common connections in logic circuits (i.e., Vcc is often applied to BJT collectors, Vee to BJT emitters, Vdd to FET drains, and Vss to FET sources). This notation then carries across to integrated circuits" Eric Seale and Wilf Rigter.
Its source: http://encyclobeamia.solarbotics.net/articles/vxx.html
and the table from there:
| BJT | FET | "Vxx" meaning |
| Vcc | Vdd | Positive supply voltage |
| Vee | Vss | Negative supply, ground |