I'm not itch.io staff - but I can answer you - 

Payment Processor Fees are the fees that Paypal / Stripe or credit card companies charge to process the payment and this happens when  someone buys your game / asset with paypal.  Itch.ios receive the money and are charged those fees  - all of which are forwarded to your account.

Payout Fees are when you withdraw the money into Paypal and Paypal charges a fee for this.  Initially itch.io were covering these fees -  but that wasn't viable for them so they started charging those fees to our accounts as well.  This may be why it's reflected under "adjustments" and doesn't yet have its own category.

Adjustments can further be where sales were cancelled or refunded after they were paid.