As for the input DC bus, standard bus capacitors should provide sufficient filtering to measure input power with multimeters, as suggested in previous comments. Typically, the voltage and current measurement of the used lab supply would do the job. If you have already 2 stage LC output filters, which isn't mentioned in your initial post, I don't see problems to measure the output power with an oscilloscope.
Voltage measurement over a precision and low inductance power resistor would avoid usage of your apparently problematic current probes.