Auxiliary 5V supply in parallel w/Arduino

I think I know the answer to this, but I'll ask it anyway:

My project has several relays and other devices that I expect to exceed the current capabilities of my Arduino Uno board, so I plan on connecting a separate 5V wall wart to power the devices independently front the Arduino supply.

I found out that the 5v 'rails' on prototyping board I bought (Adafruit Proto Shield for Arduino PCB [v.5] : ID 55 : $6.00 : Adafruit Industries, Unique & fun DIY electronics and kits) are already connected to the 5V pins on the Arduino, so I connect the +5V wire from the extra supply, it will be connected to the 5V Arduino output. Nominally, it shouldn't matter - +5v on either side, no current flows, but in reality, I'm thinking it's a bad idea. Am I right in this?

Only the GNDs between the Aruino and the wall wart should be connected.
Do not connect the wall wart +5V to the Arduino +5V!
(Unless you are sure the USB cable or the onboard regulator (VIN cct.) is not used)

Yeah, that's what I was thinking. Was just kinda hoping I was wrong! I think I found a trace I can cut on the proto board to separate the two supplies.

If there are two holes (at 1/10th inch) with the trace between, you could put a 2 pin male header in them and short them with a shorting plug later when you need to.

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Thanks - good idea. Think I have a few extra jumpers lying around…