Prices depend on when there might be a promo or coupon code.
Some USB Testers that aren't too expensive and offer pretty good precision might be:
1) Juwei J7-4T USB OLED Display Tester(there are various re-brands of this) ~$13.92 (with $2 AliExpress coupon)
review here: https://lygte-info.dk/review/USBmeter%20USB%20OLED%20display%20tester%20J7-4T%20UK.html
what I like: reversible male-USB so I can plug anyway for right-side up
2) RD AT34 (was $6.99 BG pre-order price about 2 weeks ago, but it's now around $10) ~$9.99
(also available from Banggood, check whose prices are better)
3) RD UM25C (UM25 w/o Bluetooth connectivity) ~ $17.50
4) RD USB 3.0 Comprehensive USB Tester (this is the highest model in that series) ~ $12.50
review here: https://lygte-info.dk/review/USBmeter%20RD%20Tech%20USB%203.0%20tester%20UK.html
other functions: USB mode can be changed to "no USB data mode, battery charging mode"
I think there may be others with more than 2 digits precision, but I'm not sure how are their accuracy and precision. The ones above are probably better than the generic ones..
Based on my experience (since I’ve got several ones, my early models were the cheap ones which have poor precision and poor accuracy, and somewhat poor contact with the USB port — eg. my first USB meters were the KWS-V20 & V21), some USB Testers make poor contact and also introduce a fair amount of resistance, reducing the max current flow.
However, the better ones seem to reduce current only a little (I haven’t had time to make a study of those in a more controlled environment, so these are observations more based on my regular usage)
I’m trying to compare my other USB meters with the YZXStudio ZY1276 (I’m presuming this is the most accurate meter that I currently own), so I compare the voltage readings and the current readings using an Anker charger (which has a fairly stable power output). Unfortunately I don’t have a benchtop power supply for making more accurate testing though.
the biggest problem of those is that they reduce the max current flowing out of an USB hub
without the testers it is about 2A with between 1 and 1.5A
Really? Why and how do they reduce the current?
A meter doesn’t directly affect the USB power supply, but if there’s too big of a voltage drop on the device end it might drop the charging current automatically to bring the voltage back up closer to 5V.
Playing with a couple of my USB meters I was shocked to find out the Keweisi I thought was the best was limiting current to about 500ma and the el cheapo with a single display that flashed between V and A did 1.2 amp. Turns out my LG phone wants high current when the battery is low and the phone is on.