Every switching circuit needs the caps.

Think of the internal circuits of the output pin either PIC or a TTL circuit. It conducts Vcc to the output then this transistor is put in off state and the other to the ground is switched on.

In an ideal world this is what should happen. But the world is not as ideal as we wish to be, so there is a small fraction of time where these two little transistors conduct at the same time producing a power drop.

You can see this in the scope clearly. Put the capacitor and all will be much cleaner. Power source has little to do with this, batteries being better in that they do not try to correct the drop by raising the level and then producing overshot.

Hope is more clear now.

So, bottom line:

Whatever you do use always capacitors!

Ioannis