472kHz WSPR RX

At about 1930z, I turned on 472kHz WSPR RX using the earth-electrode "antenna" in the ground. So far, no spots. It is now 1952z. 

I notice the noise floor on 472kHz with the PC charger on was S8, whereas with the charger off it is S2. As WSPR bandwidth is only about 6Hz, I wonder what difference this makes? I am no theory man, so I do not know the answer.

UPDATE 2210z:  5 different stations spotted this evening with the furthermost LA8AV (1012km). I shall shortly be turning off the gear.