From Path of the Vampire Wiki
PXP – short for Power Experience Points – is what you use to buy powers for your character. You can access the Powers page via the right drop-down in the top left corner of your screen. Your PXP available will be at the top of the powers page.
For Vampires, PXP is gained if you have 10 blood or more at the day change, which is midnight EST (and 8 hours before sunrise, which you can check by looking at the red countdown on the bottom right of the game screen). If you have 10 blood or more then, you will gain 1 PXP for that day.
For Paladins, PXP is gained at day change if the character's remaining anima is 6 or greater at that time.
For Sorcerers, PXP is gained at day change if anima has been expended during that previous day. Anima can be spent via the 'use power' (the lightning bolt) on the right side of your grid screen. If anima is expended via use of battle power (when fighting an NPC or battle to the death with a PC), this also counts towards PXP gain. If any anima has been used on a power prior to day change, the sorcerer will gain 1 PXP at day change.
Blood Thieves gain PXP for every day they have vampire blood in their system. This means if they have Duration 1 (meaning they only keep vampire powers for 1 day), they would only gain PXP for a single day after they feed. They would thus need to feed again to gain more PXP.
You can buy a PXP Orb at any magic shop or Karma shop. These orbs cost 10 karma and can be purchased with in game money for $300,000. Normally, you can only buy three orbs per month*(when the 1st day of the next month arrives is when you can buy new orbs). However, if you have been on hiatus, vacation, etc., you will be able to purchase PXP orbs up to 50% of your total losses (in the past month). This is a catch-up boost. The limitations on PXP Orbs are in place whether you are purchasing with karma or in game.
A PXP Orb will give you 10 PXP.
Fade Absorption is a Fadewalker Power that allows you to find PXP Orbs in the Shadow Realm and sometimes in the real world, although these orbs are very rare. Found orbs will only give you 1 PXP per orb instead of the 10 PXP for a purchased orb.
There are a fixed number of these that spawn each day, which means they will not respawn once they are all collected, nor do they roll over into the next day if they are not found.
Fadewalkers with Fade Absorption 2 have a 1 in 7 chance to gain an extra PXP at day change each day.
Fadebeast Tooth Necklace
If you buy a Fadebeast Tooth Necklace relic you will gain one extra PXP on the first day of each month.
You will gain 1 extra PXP per day that you get your energy down to less than 5 points at least once a day. This does not work for those who have been in training squares that day.
PXP is spent on gaining powers; all path powers and bridge powers have the same cost pattern. More details can be found about costs on the Powers page. Details for costs of human powers can be found on the Human powers page.
PXP may also be spent to gain EXP at a ratio of 300:1 (300 EXP gained per each PXP exchanged).