Let's say speed is 25 in all examples. To differentiate between horizontal movement and horizontal leap, I will call them ''Long Leap'' and ''High Leap''. This will come in handy when we look at the interactions with Powerfull Leap.
''Long'' Leap(1 Action): 10 feet horizontal
''High'' Leap(1 Action): 3 feet vertical, 5 feet horizontal
Long Jump (2 Actions): DC 15-25: Sucess: Move a number of feets horizontal = to the DC you selected for the check, up to your speed. In this case: 15 to 25 feet on a success, 10 on a failure
High Jump (2 Actions): DC 30: Sucess: 5 feet vertical, 5 feet horizontal.
Let's note that the jumps are written in a way where they can only go to the to the same category on a failure (High Jump fails into High Leap, Long Jump fails into Long Leap)
Now, let's read the whole entry from the feat:
PowerFull Leap
When you Leap, you can jump 5 feet up with a vertical Leap, and you increase the distance you can jump horizontally by 5 feet.
This is the contentious part. Because ''High'' Leap also has horizontal movement there is 2 readings possible there:
1) When you ''High'' Leap, increase the 3 vertical feets to 5, and the 5 horizontal feets to 10.
or
2) When you ''High'' Leap, increase the 3 vertical feets to 5, and when you ''Long'' Leap, increase the 10 feets to 15.
Because High Jump and Long Jump are modified leaps, it seems Powerfull Leap should aply to them. (You are doing a modified, modified leap) For the following results:
Long Jump: Move DC + 5 feet horizontally
High Jump: 5 feet vertical and 10 feet horizontal on a success or failure.
TLDR: Does the Powerfull Leap feat increase both the vertical and horizontal part of ''High Leap'' ?