I can share the differences between PSM, PSPO and the PMI-ACP, as I attained all three. All three are worthwhile, because you gain a lot of knowledge in preparing and studying for them. Think of PSM and PSPO as being deep in the role and Scrum only, whereby the ACP is wider, broader and more general Agile related concepts.
The PSM and PSPO, both from Scrum.org, are focused on the specific Scrum Master and Product Owner roles respectively, and only test you in Scrum specific topics. These two exams go much deeper into Scrum than the ACP. The specifics can be found on this web site.
The ACP from the PMI is much broader and more general than Scrum, focusing on Agile principles, values and mindset, and does not focus only on Scrum, but includes Kanban, Lean and XP. For the ACP you have to understand adaptive planning, stakeholder management, value driven delivery, problem detection, and continuous improvement concepts. You wouldn't get a lot of Scrum related questions.
ACP requires you to take a course, fill out an application, document relevant work experience, and take the exam at a test center. If you want to take PSM or PSPO you can choose a course or just pay a small fee and take it online. PSM and PSPO are yours forever, but you have to renew your ACP every 3 years. ACP is also more expensive.
ACP is a 2 hour testing , with ~150 questions. PSM I and PSPO I are one hour, with fewer questions.
PSM and PSPO also have advanced certifications, whereas ACP does not.