The 3.3 V budget

One small regulator

Both 3V3 positions are fed by the same part: U13, an XC6206P332MR, a 3.3 V regulator in a three-pin SOT-23 package, three millimetres long. It takes the 5 V rail and holds 3.3 V at its output.

Torex's datasheet gives it a maximum output current of 200 mA, and a dropout of about a quarter of a volt at 100 mA: it needs its input only that much above 3.3 V to keep regulating. The 5 V rail is well over a volt above that, so the 3.3 V holds steady even when the 5 V sags.

Shared between both sides

That 200 mA is the regulator's, not each side's. With both switches on 3V3, the two sides draw from the same part, so add them up.

What fits comfortably:

• sensors — a BME280, an SHT31, a light sensor — a milliamp or less each;
• a small OLED, a few tens of milliamps;
• a handful of LEDs through their resistors.

What does not: a Wi-Fi microcontroller. An ESP32 transmitting pulls well over 300 mA in bursts, and the regulator cannot follow. The 3.3 V rail dips during each burst and the ESP32 resets.

Feed a dev board 5 V instead

A dev board has its own 3.3 V regulator, sized for its own chip. So set one side to 5V, wire that rail to the dev board's 5V or VIN pin, and let the dev board make its 3.3 V. The adapter's 5 V side is limited only by the half-amp fuse, and the dev board's 3.3 V pin can then power small parts beside it.

Keep the standard board's 3.3 V side for the parts that need little: the sensors and displays that make up most of a breadboard.

Heat

A regulator like this one makes 3.3 V by turning the rest of the input into heat. At 4.7 V in and 150 mA out it drops 1.4 V, which is about a fifth of a watt. Torex rates the bare SOT-23 package for a quarter of a watt on its own, so near the top of its current rating it runs hot. It will not fail quietly — it limits its own current — but a hot regulator is a rail about to sag.