Laptop to "Desktop" Conversion
Acer has weird, but not necessarily proprietary connectors. If you have an electronics shop nearby, your best bet is to bring the laptop there and try until you find a matching one.

Desoldering a connector on a mainboard is a semi-difficult thing, because these are usually connected to large copper planes, so you need a high-powered soldering iron with good temperature control.

It is definitely easier to change the connector on the power supply than on the mainboard, though.