Below are screenshots from some quick testing. On a char with Enhanced Power Attack from Frenzied Berserker. I didn't test it with a bludgeoning weapon. The issue persists both with shield equipped and not equipped. However, with no shield and a two-handed weapon the damage bonus from Powerful Charge isn't applied at all if any Power Attack mode is enabled. It is applied properly in this scenario if no Power Attack mode is enabled as per testing described below.
PA = Power Attack
PC = Powerful Charge
No weapon, shield equipped, PA 2 enabled. First screenshot, +3 bludgeoning damage bonus from PA is present. Second screenshot, it is still there, with +1d8 slashing damage bonus from PC while charging.

Slashing weapon, shield equipped, PA 2 enabled. First screenshot, +3 slashing damage bonus from PA is present. Second screenshot, it is replaced with +1d8 slashing bonus from PC while charging.

Piercing weapon, shield equipped, PA 2 enabled. First screenshot, +3 piercing damage bonus from PA is present. Second screenshot, it is replaced with +1d8 piercing bonus from PC while charging.

Slashing weapon, shield equipped, PA 6 enabled. First screenshot, +9 slashing damage bonus from PA is present. Second screenshot, it is still present, but the 1d8 slashing bonus from PC while charging isn't added.

Slashing weapon, no shield equipped, PA 2 enabled. First screenshot, +6 slashing damage bonus from PA is present. Second screenshot, it is still present, but the 1d8 slashing bonus from PC while charging isn't added.

https://postimg.cc/D48KfNM7
https://postimg.cc/rzmT9dF7
https://postimg.cc/QHKrRR7b
https://postimg.cc/PLTsvJR3
https://postimg.cc/bGgXx8Xz