N Cook wrote:

I need to get a rough idea of the amperage capability of a small 5V SM ps
before attaching it to its load, to simulate, just in case the regulation is
kapput.

A single output 5v smps? A "guesstimate" would be to multiply the input
power by 0.6. If the input was 2a @ 115vac, the 5v output current would
be *in the ballpark* of [(2 x 115) x 0.6] / 5 or *about* 27 amps DC.

The rated input current *should* be on the PSU label.