Try to plug in a microUSB cable connected to a USB adapter to power RPI additionally with USB power. The issue is not with 40VA power adapter, the issue is that when OSPi was designed, it was only meant to drive 0.5 to 1amp on 5V line, and since then the new RPIs each version keeps requiring more current so it can’t keep up. Providing USB power to RPi directly should address this issue.