You card needs a minimum 180 Watts power input. Going through eXtreme Power Supply calculator and using a minimalistic requirement show that at the very minimum you need a 516 Watt PSU. I'll link to the page but I don't know if it will go back to default. If it does input your hardware and see what comes up. Then physically check your PSU rating inside the case. If ok then we'll have to thinks of something else.
Surface Pro 5 News - release date, UK price, features, specs