Hi @Bernad SyncMaster SA,
Here’s the [https://download.lenovo.com/ibmdl/pub/pc/pccbbs/mobiles_pdf/t520_t520i_w520_hmm_en_0A60078_08.pdf|hardware maintenance manual] for the laptop.
On p.153-154 you will find the parts numbers (FRU no.) for all the different AC adapters that are used with the model series.
Locate your specific model variant in the list to find the part number and then search online using the part number ''only'' to find suppliers and the cost of the part.