Instead of the AC adapter (or AA batteries), can I use a USB to 12V convertor to power my reface from the USB charging port on my amp?

Yes you can - BUT - you will immediately void any warranty that may still be in force and you take all of the risk of any damage that may occur if the unexpected happens.

There are at least three realities at play here:

1. All Yamaha manuals I have seen, including Reface, include a warning NOT to do that.

https://usa.yamaha.com/files/download/other_assets/6/438816/reface_en_om_b0.pdf
This product utilizes batteries or an external power supply
(adapter). DO NOT connect this product to any power supply or
adapter other than one described in the manual, on the name
plate, or specifically recommended by Yamaha.

WARNING
• Be sure to use only the correct AC adap-
tor (page 48). The use of other adaptors
may damage the instrument, cause it to
overheat, or create a fire hazard. In such a
case, the product warranty will immedi-
ately become void, even if the warranty
period has not yet expired.

2. Twelve volts is twelve volts - as long as the adaptor produces a steady, reliable 12 volt supply and has adequate isolation of transients there is little risk.

3. Some low-end adapters do NOT have adequate isolation of transients and thus have the potential to damage the instrument. Transients can include both voltage fluctuations as well as pass-through AC modulations on the DC power.

You should have no trouble if you use a medium-grade to high-grade adapter but you need to consider how much risk you want to take.

My suggestion is to buy a good quality backup power supply that has a couple of protected AC plugs to supply power. You only need 6 watts of power.

USB Port (5V) --> 5-to-12 converter (assume some amount of inefficiency. I see 80% for one) --> 12V @ 0.5A (this is 6W)

6W / 80% efficient -- or 0.80.= 7.5W

W=VI, so 7.5W=5volts*? Amps, Amps = 7.5W/5V = 1.5A

... so, assuming 80% efficiency of the 5-to-12V regulator you would need your amplifier's USB port to be rated at at least 1.5A (above is fine, below may cause voltage droop and other problems).

I don't know your amplifier's USB port output power rating - so I don't know if you have the juice to do this or not.

I also don't know how (in)efficient your 5-to-12V converter is. That plays in the calculation as shown above assuming 80%.

The warranty isn't automatically voided by using something other than the PA-130. The warranty is voided if damage occurs due to using a different supply. The quoted warranty information mentions "in such a case" -- and the case is when there is damage due to the off-broadway power source (i.e. it's your gamble).

Outside of the efficiency of the 5-to-12V converter - I'm not sure how "clean" the output is. And by this I mean the AC component on the DC voltage (such as ripple). In this case, I don't know what the Reface can tolerate and characterizing this would probably need test equipment since the converter is not likely to self-report this property. Nor would I necessarily trust all sources of this information (depends on the manufacturer for me).

By no means is this a slam dunk. It's feasible like water skiing behind a cruise ship is feasible (or pick something less drastic).

Also the above is based off assuming the Reface's draw of 6W on 12V. The power supply that is, well, supplied with the Reface is 12W @ 12V capable. So it can source double the rated draw power of the Reface. The calculations above are assuming no margin above the draw of the Reface. You can add your own derating if you want to the calculation (which would end up with a higher-than-1.5A requirement on the USB port).

Let me throw a curveball in this discussion - this USB-C to 12DC cable has a chip that "negotiates" up to 3A of power from a USB-C PD source:

https://aliexpress.com/item/1005003627540013.html

The key here is to use a USB PD (Power Distribution) adapter.

I am using an Alto UBer FX portable PA and the USB charging port is only rated at 1 AMP, so based on your analysis, probably would not be strong enough to power the reface and I could damage it to even try, right?

Here is a link for the product advertised to work with the Reface. Of course, it would still require the right USB power source to drive it. I don't know if my Alto PA USB port would work. If not, when AC is not available, I might be content to simply bring a bunch of AAs.

RipCord for Reface

The warranty isn't automatically voided by using something other than the PA-130.

While I certainly respect your opinions on this topic they are in direct contradiction to Yamaha's stated requirements which I quoted in my reply.

DO NOT connect this product to any power supply or
adapter other than one described in the manual, on the name
plate, or specifically recommended by Yamaha.

Your statement is only correct if that 'something other than the PA-130' has been 'specifically recommended by Yamaha'.

The quoted warranty information mentions "in such a case" -- and the case is when there is damage due to the off-broadway power source (i.e. it's your gamble).

That is NOT the only case Yamaha's statement mentions

The use of other adaptors
may damage the instrument, cause it to
overheat, or create a fire hazard

Any or ALL of those are legal grounds for Yamaha to consider the warranty void. If Yamaha says your
'non-recommended' adapter caused the instrument to overheat you would have a 'tough row to hoe' to argue otherwise.

Here is a link for the product advertised to work with the Reface.

Keep in mind that 'advertised to work with' is NOT the same as 'recommended by Yamaha'. Any resulting damage/destruction of the instrument will be your sole responsibility.

If not, when AC is not available, I might be content to simply bring a bunch of AAs.

That will certainly do the job.

Another idea is to get two sets of rechargeable AA batteries and a USB adapter to power a device that recharges AA batteries.

Then when batteries you are using die you can use the backup set of batteries and recharge the first set.

Only you know ALL of your requirements and power needs - such as what source of power you plan to use for your USB power scheme.

If it is your car then I still like my first idea of buying a UPS power supply that you keep charged and in your car. Then no matter where you are you have enough power to recharge your phone, use your laptop and wifi or power your reface.

I always carry a fully charged UPS in my car just for emergencies. Thankfully, I've never needed it but I'm glad to know it's there if I need it.

And you can always use the UPS at home or at your 'cabin in the woods'.

The RipCord AA928MS shows 12W @ 12 V. Then on the 5V side it shows 3.0A max which assumes full 12W output on the 12V rail. Running the numbers, P=VI. P=5V*3.0A = 15W. 12W(regulator output)/15W(regulator input) = 80% efficient. Which matches my earlier assumption. Note RipCord has another 12V model that is only 75% efficient.

Therefore, all of my calculations from before stand and if your reface draws the rated max (0.5A on the 12V rail = 6W) then a 1A rated USB port is not going to be sufficient to cover the max power case.

Your reface's power consumption when you use it may never get close to the maximum rating. I don't know how much margin is in the spec and this would be "max" vs "typical".

I take it because RipCord advertises Reface compatibility that the quality of the output is fine -- it's just down to if your USB port can power it or not. The absolute maximum the RipCord (this one) would draw needs a USB Port capable of supplying 3A @ 5V. 3A, incidentally, is the maximum current for any USB Type A connector (the kind this RipCord plugs into). Under fault conditions (of the load - i.e. Reface) this RipCord may draw its maximum 3A. The USB port on the amp would need to have overcurrent protection or else I would expect this would damage the amp in this (corner) case.

I understand and will follow your advice and order a good set of high capacity rechargeable batteries instead. Maybe 3300mAh? Are there any concerns I should take into account with this?

Just don't mix batteries and make sure the voltage of them matches AA (1.5V-ish). There are rechargeable batteries that are the "same size" as AA but are a different voltage.

If I was willing to use a RipCord power cable - I don't see the difference (in practice) of using a power adapter. That's what I would do. And I'd carry a small power strip with maybe 3 slots for my amp and reface power supply to plug into. Then put an extension on the power strip so the amp + reface power brick can be located as far away from the power outlet as your amp currently can.

My gear I leave the power strip connected to my power cables (going to gear -- at least the ones that are removable) and extension cables so it's not any more setup time at the gig or break down.

Thanks for all this info and advise.

Jason , i see that you are very educated about the subject so i want to ask. I have same question as OP , i know i can use batteries but i want to find out powerbank option more here are my powerbank specs

removed link - main option , removed link - secondary one 

removed link   - here is reface DX adaptor specs 

Will generic (not cheap one) cable  that u power router  from power bank work?  something like 12V ,1A or 2A

Or should i get one with different specs? 

I am bit of a dummy when it comes to this thing so it would be great if you would give me answer to this, thanks in advance

For some reason links to pics got removed , so here are the specs :

1st power bank - output :5v=3A or 9v=2A or12V= 1.5A ,

2nd power bank -5V = 2.4A 9V=2.5A Max, 12v=1.85A Max

Reface adaptor  - input:120v - 60Hz 0.3A

output: 12v - 1.0A

I'm wondering what switches the voltages of the power banks?  A manual switch that you slide to the 12V position?  Or something else that sets the output voltage?

Assuming you can fix either to 12V manually, then either seem to be able to supply the amount of amps needed.  I'm going by your listed 12V @ 1A spec of your Yamaha reface official adapter.

Since you couldn't link your "power bank" models (and, frankly, I don't know exactly what that is without more specs) I'm not sure where these banks get their power from.  You say they're not batteries so I assume they plug into an outlet for their power source.   Correct me if that isn't accurate.

What I would be most concerned about in all cases is polarity.   Since this is 12VDC you have to get your positives and negatives matching.

Sometimes you will see a sticker or silkscreen or embossed plastic (or manual) that would document if the inside pin is positive or negative.   If that isn't documented then I would use a multimeter on the original power supply to determine which side (pin/inside or barrel/outside) is positive.   And make sure your power bank polarity matches.

If you aren't sure about polarity then I would advise not to hook up anything but the official adapter.

I'm not endorsing you to use anything other than the official supply because right now I don't have sufficient information to know that what you're wanting to use is fit for function.

And again, my solution would always to use the power brick that came with the unit and a power strip and extension cord to reach an outlet up to 15 feet away (or whatever length your situation demands).  I carry all of this in a backpack along with 1/4 inch cables and XLR ... and pedals ... and ...