Hi @maroloplubis
Here's the [https://download.lenovo.com/ibmdl/pub/pc/pccbbs/thinkcentre_pdf/0b03457.pdf|hardware maintenance manual] for the model.
Go to p.102 of the manual, to view the procedure to remove/replace the power supply unit.
Go to p.133 to find the FRU number (part number) for the power supply. Search online for the ''FRU number only'' to find suppliers that suit you best.