the OEM power supply usually does not offer proper power connections.
and the majority of these old RX 550 cards require at least 300w, some up to 400w.
upgrading to a retail power supply is also usually not possible due to case size,
OEM motherboard connections,
and other restrictions.
these OEM prebuilt systems do not usually fit retail components.
and usually have terrible airflow so heat can be a big issue using them.
you would probably be much better off starting from scratch and building a real system rather than continuing with this thing.
and just a question,
do you have some problem with your vision that you need to use ridiculous oversized fonts?