Those are 4mm shrouded banana connectors. They are seen on electronics lab equipment, such as power supplies, multimeters, test probes with removable leads and various other (sometimes custom) gear. It's basically the go-to connector when you need a touch-safe single pole connector for lab use.
Plugs, both straight and stackable and readymade leads are available from most good electronics suppliers, search for "4mm shrouded" and you should fine them.
You can plug an unshrouded banana plug into a shrouded socket and this is a reasonable thing to do if you are working at safe voltages.
Contary to lyncas answer, you can't directly use bare wires with your power supply. Many power supplies come with binding posts that can take either bare wires or a 4mm connector, but yours is not one of them.
In my experiance lab power supplies normally have either 4mm shrouded sockets (which can take either shrouded or unshrouded 4mm plugs, but not bare wires) or "binding posts" that can take either bare wires or unshrouded 4mm plugs but not shrouded 4mm plugs. I have occasionally come across power supplies with binding posts that could take shrouded plugs but they don't seem to be common.