That looks too small for 1uF 100V, and generally a terrible idea. They might have just put in whatever was lying around as a bodge for a common-mode noise problem but it's a linear PSU? There should be two caps, one for each channel?
1652 (digital) and 1651a (analog meters) might be similar to 1651.
BAMA has the B&K 1651 schematic but no sign of Y-caps. I wish that site was indexed by search engines, they completely miss it.
I let my bench PSU's (output) float noisy with hum etc. OR direct earth-ground OR 1MEG/22nF Y-cap 275VAC if I need to float with less CM noise. It depends on the power transformer's winding capacitance. B&K might have bungled the electrostatic shield.