Registered mail by USPS is as safe as I can find.

I have had items come up missing with USPS that had tracking and ins. Put in tickets and ended up never getting the item returned and only refund of shipping/ins.

If its anything I'm scared to lose I send Fedex or UPS. I think issues are geographical based lots of times. Meaning my local USPS are not on the ball where my Fedex or UPS are. From my location its almost always cheaper to send through Fedex or UPS with quicker guaranteed delivery dates.

You should be worried, but what'cha gonna do?

Insure for the loss, be prepared to document the nature of the item in case worst comes to worst.

I've had last-of-it's-kind-in-the-known-universe items destroyed by shippers.

I've had impossible to replace things lost by shippers.

I don't have his card anymore, but I had a few pieces picked up about ten years ago by a guy whose whole business was the ultimate white-glove delivery service for high end antiques and jukeboxes and pinballs. He had a super-cushioned ride enclosed trailer, used 6" of foam and blankets on every side and padding underneath, personally put everything on his trailer and personally unloaded it when he got there. One guy, a couple helpers, personal accountability.

Just the person you'd want to deliver your James Bond 40th pinball!

Lately, (since covid) I've had shippers lose over a dozen packages at USPS. It's dropped off at the post office, but it never goes any further. Gone forever. Certain post offices are not at all reliable shipping locations... others haven't ever had a problem.

I've been watching what High End Pinballs does when he ships... He seems to be doing all he can on his end to make the shipping experience perfect.

Agreed. But in my instance it was paying more for less. USPS is 2 minutes from my house but I now drive 20 minutes to ship Fedex or UPS.

After a bad experience with FedEx in which they tried to lowball the value of my high-end camera lens by using their own 'depreciated values' after they misdelivered it and ignoring the true value (going ebay prices and price I sold it at) of it, and seeing how the drivers drive and behave in the neighborhood, I don't trust them to anything.

Just beware that your 'value' may not be their 'value' if something happens to it.

Yea this can happen with all shipping places

Yes. Pack it really, really, really well.

A scrap of bubble wrap and a flimsy box won't do it.

Basically, wrap it like you would expect someone to drop it, kick it, trip over it, use it as a step stool, or tap dance on it.

Back in the day, somebody in America needs a transformer for a "The Empire Strikes Back"
I had one that I did not need, I knew he would not find one locally, so I sent it off
The post office asked if I wanted insurance, but how do you value "unobtainable"?

Figure out what it would cost to make one?

Or figure out what one would sell for on the open market?

I've never had that happen. Poorly packed items that don't give structural support to the box have a higher chance of the box being crushed and shredded and then losing the label.

Also make sure the label is protected from water with a layer of packing tape.

If you are worried about losing a package, put the shipping & return addresses on multiple sides of the box, and also tape it to the item's packaging, or a couple layers inside the packaging.

Also make sure the address is legible. Don't hand write it--only use printed text so there's no room for interpretation.

Insure it for the cost of having a custom toroidal transformer built… around $300-450.

Pack well, get tracking of course, but also make sure it's sent signature required and you should be fine.
You can can only control what you can and hope for the best. It's a bit scary but the odds are in your favor that all will be good!

Put an Apple Airtag in the box.

You will know more about its whereabouts than the shipper