I initially wrote that Edworthy Computing fitted an old and dusty power supply instead of the new one, with a £27 charge for the power supply and £55 for labour. Edworthy Computers promptly phoned me up the following day, apologised, and explained that the shop assistant had failed to pass on a message: "that a reconditioned power supply had been fitted temporarily until the new power supply arrived, and could be exchanged now that the new one had arrived". It is a pity that this message wasn't passed on at the time the computer was first collected with the reconditioned power supply fitted. They've now fitted the new power supply which I'll inspect when I return home to Devon.