First, do you know for a fact that a standard power supply will work in that computer? A lot of the Lenovo computers I've seen using special connectors between the power supply and motherboard. I'm talking about the 4+4 pin power connector and the 20/24 pin, those are the standard. You will know just by looking at your computer's motherboard if it has them or not.
If it does, then a good brand like EVGA will work. Something in the 450W-500W range should do, and make sure it has the 6+2 pin pci-ex connector.
edit:
matunders :
I bought an atx adapter 24pin to 14pin adapter so I’m open to any psu
I have to admit, the idea of using adapters bothers me. The idea of using adapters for power supplies really bothers me. I'm not saying it won't...