Provided are a power supply device capable of supplying required power even during standby and an electrical apparatus. A power supply device includes a current resonant circuit configured to drive a transformer and a resonant circuit using a switching element, the resonant circuit being connected to a primary side of the transformer, the switching element being periodically repeatedly turned on and off, and a controller configured to control the switching element so that the switching element performs a continuous operation in which the switching element is turned on and off continuously repeatedly or an intermittent operation in which the switching element is turned on and off intermittently repeatedly, in accordance with an external signal indicating the continuous operation or the intermittent operation.