ATX stby voltage too low +1.8v

hi members !
Got fuj. siemens esprimo c5910 with power issue : no reaction to switch.

To make pc start, need to power up PSU alone without load (by grounding pson) before connecting it to mobo

All PSU voltages are checked ok without load (stby voltage=+5v), but when connected to mobo, stby voltage becomes low : 1.8V.

Steps taken : swapped PSU with a good working one, pc starts normally.

Concluded that PSU is culprit, and particularly stby rail.

Opened PSU case, all caps are looking fine.

Any idea as what are the common main stby rail check points and where to dig further to help fixing this issue ?

Unfortunately no schematic available for PSU model : NEWTON POWER LTD MODEL : NPS-210BB A REV : 08 -210W

Thank you

That's a pretty old PC. PSU is only worth $33 on EBAY.
+5Vsb is usually <2A. so if +5Vsb drops to 1.8V from say 1 A load that implies ESR of cap is (5-1.8)/1A=3.2Ω This is too high for a low ESR cap, but might not be high enough to cause bulging from heat but it should get hot.

trace the heat or the voltage or the track and replace the Cap.