Manufacturers usually report ESR at either 120 Hz (or 100 Hz) for mains-frequency rectifiers, or higher frequency (such as 100 kHz) for switching power supplies.
That large capacitor is probably above resonance at 100 kHz, and should be measured at 120 Hz. What is the Sprague spec for 120 Hz ESR? Note that the reactance of 330 uF at 120 Hz is 0.25 ohms, so an ESR of 0.1 ohms will have a small, but measurable, effect on the filtering.
A good freeware tool for designing conventional power supplies is 'PSUD2' from DuncanAmps.
https://www.duncanamps.com/psud2/index.htmlIf the capacitor in question is across the output terminals, it probably is not the cause of your ripple. Either there is a fault in the feedback amplifier (a "speed-up" capacitor is one from the output directly to the amplifier, bypassing the resistive divider), but more likely a fault in the rectifier or main filter capacitor. An oscilloscope (connected very carefully) is the best way to trouble-shoot this.
Vishay now makes the old Sprague 659D series. Your part number seems incorrect (or obsolete), since there should be only 3 digits after "659D", giving the capacitance. In the current Vishay data sheet, at 120 Hz, the
maximum ESR value for 330 uF capacitors ranges from about 0.5 ohms (35 V rating) down to about 0.3 ohms (200 V rating). see
https://www.vishay.com/docs/42039/601d.pdf