How much current can an externally powered USB3 hub supply to each port?

Problem Description:

• I have a WD My Passport 4TB 2.5" USB3 HDD (bus powered). I've been using it as network drive connected to the USB2 port of a Pi3 for 18 months now.
• Over the last few months I'm hearing clicking sounds and I've had to "Check" the filesystem in Linux GParted. That fixes things for a while but the clicking is still there. Once or twice the drive became unusable and it had remounted itself as read-only.
• I'm guessing that I should have been connecting it to a USB3 port and maybe also externally powering it.
• I read that external USB drives draw max current at spin up. I could not find information about this for the WD My Passport drive but I read that some can require up to 1.2A on spin up.

My Question:
I'm thinking of getting this Ugreen USB3 hub as well as a 5V/3A power supply and maybe a new WD My Passport 4TB 2.5" USB3 bus-powered HDD as well! Let's say the WD My Passport drive does use 1.2A at spin up.

1. If I use an externally powered USB3 hub will the drive get enough current required during spin up or will it still be limited by the USB3 spec of 900mA per port?
2. If the limit is always going to be 900mA per port then why do manufacturers make bus powered USB3 drives that may require more than 900mA?
3. What would be the best solution for me? I thought of switching to a Sata SSD connected to a Pi 4 USB3 port since they require far less power at all times? I have a 1Gb LAN which I read will limit the speed benefit of SSD accessing it over a network but they are more reliable than HDDs it seems?

Thanks.

What comes to the old HDD, the clicking sound means it's already failing. And the fact it's already become unusable means it's going to die altogether sooner rather than later.

1. Whether or not any given hub is able to pass more current than the nominal 900mV is down to the construction of the hub itself. According to Wikipedia USB3 ports can, if needed, provide additional power as they can implement other USB specifications like USB Battery Charging Specification for power up to 1.5A or 7.5W. USB 3.1 can go even higher. The Amazon page of this device states that if high power consumption devices are connected, an external PSU can be used; so this shouldn't be an issue for this device.
2. Not really applicable, cf. above
3. The "best solution" depends entirely of the intended purpose and budget. SSD drives are a good option as they don't contain moving parts they're not subject to pure mechanical stress, vibrations etc.; but a 4TB SSD is easily 4 to 6 times more expensive than a HDD of same size.

Power consumtion / distribution capabilities of a given device should be available in the documentation or manufacturer's website. If they're not found, the best option is to get in contact with the manufacturer - this kind of info is necessarily public.

As to that specific UGREEN hub you linked on AMZ, you may want to find something else— Either be prepared to try it alone and with different external power supplies (and need to return one or more of those pieces), or I’d look for something more certainly robust. (But otherwise, that one looks like a fine value.)

I’m hesitant because the listing’s information on external power is very different from the Amazon.com (USA) product page, compared with the Amazon.DE product page:

- The US/EN page reads: "Wide Compatibility: USB splitter is compatible with Windows 10/8/8.1/7 / Vista / XP and Mac OS X, Linux and Chrome OS. Plug & play, no driver needed. Stable and Secure: With built-in protection for over-voltage and over-current, this 4 port USB charging hub can keep your digital devices and data safe."

- While the.DE page reads (in EN): "Great Compatibility: Compatible with Windows 10/8/8.1/7 / Vista / XP and Mac OS X, Linux and Chrome OS. Plug & play, no driver needed. With 3.5mm x 1.35mm DC-Jack, if you connect high power consumption devices (more than 900 milliamps) HDD, power supply can be connected to offer extra power (power adapter sold separately, available by ASIN B00TAILRR8)."

That’s confusing because the product-images seem to show only a rear microUSB input, which seems to be confirmed by one (US) reviewer, who complained that the cited external power supply is the incorrect plug size: “’AC to DC Adapter 5V 2A Power Supply Adapter with 1.35mm x 3.5mm Connector Plug’ No, no you don't. THAT IS THE WRONG DAMN CONNECTOR FOR THIS UNIT! This unit requires a micro-usb to connect to the unit, not a round pin -- which is what I ordered because the ‘seller’ gave the incorrect information. Nice job...” By Amazon Customer on September 4, 2020

(I also searched for the "GL3150" chipset pictured in that drawing/image, and found this similar hub. That one specifies micro-USB power-in, but provides no other info on total available power.

And to build on/generalize what Peregrino69 said: The power available on any USB3 (or really, any port on any externally powered hub) will be bottlenecked by one of:

1. the physical power of the external source powering the hub (that is, you can't get 25 watts out of a 15watt wall-wart!); or
2. the constraints of hub's physical chip, and the hub's available protocols (even a 5A/5V=25watt wall-wart couldn't supply more power than the hub's chips and protocols allow, though it might offer more stability--or it might lose some efficiency).

And yes, back up that clicking disk RIGHT AWAY!

(I hope this is helpful-- I'm new here and can't comment yet!)