Before:

There are actually a couple runs of relatively modern grounded, albeit still old and crappy, grounded wire in my basement, including one powering my shed that ran right next to this outlet, and its shitty old ungrounded black cloth cable. I hijacked that and repurposed it for this outlet.

So, no shed power currently, but this first job gave me the confidence and motivation to tackle the rest of the house now.

And presumably you're still alive, hence this post! Kudos!

Is that metal box connected through to your electrical panel via metal conduit? If so, the box itself might be grounded, so you wouldn't need to actually steal the power from your shed. Of course you'd want to test any outlet with the tester you have, but you'd just wire the grounded outlet like normal but w/no ground cable, and make sure the upper/lower metal tabs are screwed tight against the box.

Also, congrats, that's a great achievement!

This house had literally ONE grounded outlet before I installed this bad Larry.

My life has NOTHING to do with electricity and electronics, but one day, I hope it'll have EVERYTHING to do with it. This is so cool!

Is it legal to DIY that if you're not a certified electrician?