I got a 5V 2A power supply for some hobby projects from Aliexpress store
YXD Wish for about $4. S-10-5 and the build quality good, solder blob under transformer and a solder balls on the PCB top so I cleaned that up.
Powered it up, get 5.0V but when connecting a load resistor it cratered. At 10R load which should be 0.5A, it dropped to 3.8V out and it went into hiccup mode below 5 ohms. About 1.5W output is all I can get.
I drew out the schematic and poked around with a scope. It's running slow at 31kHz and primary current pulses are measly 30mA. So I think the IC is fake and not working, it has no markings.
It appears to be a TX203H alternates are CR6203, RM6203, SDC603, SW2604, SL2128B. Commonly used in wall warts.
(The bottom rung version of this same S-10-5 using phenolic PCB, uses IC DK1203
Dongke Semi and no current-sense resistor, and cheapened other stuff.)
I asked for a refund and so far the vendor is quiet... I had another one ordered from a different Ali store but the floods took out rail and highways to the coast so it will be a while to get here and compare.
Don't forget
website comparing pinouts of SMPS IC's. Good tool to reverse-engineer the IC used when there are no markings or it popped.