Dell Latitude 5500 sudenly slowdown

Greetings, Dell Support Team.

We did buy from Amazon a refurbished one https://www.amazon.ca/Dell-Latitude-5500-Laptop-15-6/dp/B08ZL7YPS6/ (service tag: JFT30R2, express service code 43137718670)

Productivity significantly (5 to 10 times slower) decreases 1-2 times per day.
Sometimes productivity resumes normal without restarting.

Here are some things we did try

1. Restarted the laptop multiple times. Slowdown reproducible in safe mode;  
2. Updated system BIOS to 1.34.1:  
3. Update  drivers (Used Dell Support Assist, DriverGenuis, DriverMax, DriverBooster)
4. Clean fans and air vents;  
5. Run a hardware diagnostic - Ok. Victoria SSD show me S.M.A.R.T. unknown or unsupported;
6. Manage thermal performance - Best productivity:
 
Our laptop isn't working properly, 

Could it be due to a defective battery, AC adapter, or outlet?

Could I kindly ask for any help to try to fix that?