Oscar wants to upgrade his power supply on his desktop computer. He must explain to his supervisor why he needs to order a new power supply.

Which of the following is not a valid reason to replace a power supply?

a$.$ Power supply outputs $11\mathrm{.}7$ VDC to the computer.

b$.$ Current power supply does not provide enough power.

c$.$ Power supply fan has failed.

d$.$ Power supply fails.