170W Alternate with the following models：

ADL170NDC3A

The product Lenovo 170W is perfectly compatible with the product model Lenovo ThinkPad P50 20EN0012US,ADL170NDC3A :

Lenovo ThinkPad P50 20EN0012US
Connector: Square Yellow with pin inside
Outlet: 3-prong
Cord Cable: US/EU/AU/UK plug
Package includes:
1 X AC Adapter
1 X Free Power cord

http://pc-laptop.co/lenovo-power_supply-170W-p180513.htm

You may also want to see this adapter:

Lenovo 170W adapter Replacement