I have some power supplies of unknown rating. In a short answer from Rafal Powierski in How to measure max current of a power supply "How to measure max current of a power supply" (Since I cannot comment yet I started a new question) he is saying that amps (shorted) x 0,7 is roughly the rating. What if I use a variable resistance and measure the voltage drops? Is there no value e.g 5% drop to indicate that the supply is struggling?

These are sloppy ways to find the rating. Everyone who is looking for the answer to this question should do long term testing while present, checking temperatures.

  • \$\begingroup\$ It’s highly dependent on how any over current protection or fold back is implemented, but 5 % drop in voltage seems reasonable as a starting point. \$\endgroup\$ – winny Jul 19 '18 at 20:15
  • \$\begingroup\$ It depends on storage energy/load power ratio and how it is regulated. Then depends if you measure Ppk or Prms vs acceptable Temp rise. And cooling method. \$\endgroup\$ – Sunnyskyguy EE75 Jul 19 '18 at 20:16
  • \$\begingroup\$ Load regulation % V error is the inverse of output impedance ratio to load. But not an indicator of power unless you have a tolerance defined . \$\endgroup\$ – Sunnyskyguy EE75 Jul 19 '18 at 23:33

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