I would have to agree... about $43 for one that covers desktop PCI-e. So that one right there would be a PCI-E desktop motherboard tester, being sold on Amazon.

Did you get the same "power" error code with both PSUs? The one the computer came with, and the one you say tests as good?

However, according to the link at Dell, that I sent you originally, for a Dell XPS 8700 desktop from 2013 (that's when the 8700 was released), a Solid Amber means "standby" mode, and if it persists, you are instructed to listen for a Beep error code. The error code you read, was for the XPS desktops that came out in 2007 and 2008. So your 8700 should be beeping, while that power LED is Solid Amber.

You said "steady" Amber... I assume you meant that it is on, and not blinking steadily.