USB Power Testers & PD Triggers

The pocketable instrument that owns the "what is this charger actually doing?" question. A USB power tester sits inline on a USB-A or USB-C cable and reports voltage, current, energy, and (on the better ones) PD/QC negotiation traffic. Worth $30 even if you never plan to test chargers — they catch flaky USB cables and dead PD power-paths instantly. Pair with Multimeters and Power Supplies for serious bench work, and Oscilloscopes when ripple matters.

Hobby inline USB power meters

• ★ FNIRSI FNB48 / FNB48S / FNB58 — color-screen USB-A + USB-C inline meters, ~$30–$60. PD and QC trigger, energy accumulation, USB-C E-marker readout, and a downloadable Bluetooth/PC app. The 2026 hobby standard.
• ★ ChargerLAB POWER-Z KM003C / KT002 / AK001 — KM003C is the higher-end PD analyzer (~$80) with PD packet capture and a USB-C oscilloscope mode. The serious hobbyist's USB tester.
• ★ AVHzY CT-3 / CT-2 — long-time enthusiast favorite; PD trigger, scripting via app, e-load mode on some variants. Pricier than FNIRSI (~$80–$150) but very polished.
• RD UM34C / UM25C / TC66 / TC66C — the older RuiDeng inline meters; UM25C is the most-shipped USB tester ever made. PD-3.0-aware variants exist.
• MakerHawk USB testers — generic Chinese inline meters; OK for a glove-compartment unit.
• Plugable USBC-VAMETER3 — clean USB-A/C inline meter aimed at IT pros; no PD packet capture.

PD analyzers / sniffers

• ★ ChargerLAB POWER-Z KM003C — see above; captures PD 3.0 / 3.1 SOP* traffic and decodes it.
• Total Phase USB Power Delivery Analyzer — pro tool, ~$1300+, captures full PD link traffic (the right answer if you're certifying a PD product).
• Cynthion (Great Scott Gadgets) — see Logic Analyzers; captures USB Hi-Speed packets natively, useful for USB device debug, less for PD specifically.

PD trigger / decoy boards

• ★ PD Buddy Sink — FOSS PD sink board; selectable voltage, used as a "USB-C → bench rail" widget. GPL.
• YZX Studio ZY12PDN — sub-$10 PD trigger board; selects 5/9/12/15/20 V via button presses on a USB-C charger.
• CHI ZTE PD-trigger / Aclorol PD-trigger — the Amazon staple PD triggers; cheap, work fine.
• Alpha Test Lab PD-trigger boards — fancier triggers with displays.
• POWER-Z KM003C — also acts as a PD trigger source.

E-marker / cable testers

• POWER-Z KM003C — reads E-marker chips on USB-C cables to confirm rated current and Thunderbolt/USB-4 capability.
• TreedixCabler / TS-WL01 — dedicated USB-C cable testers; report E-marker info, continuity, alt-mode pin status.
• FNIRSI FNB58 / FNB48S — also read E-marker IDs.

License / pricing notes

• FNIRSI / RD / ChargerLAB / AVHzY all ship closed Windows/Mac/Android apps; Bluetooth protocols are partially reverse-engineered — community Python libs on GitHub exist for FNB48S, UM34C, and KM003C.
• PD Buddy Sink is fully open hardware (GPL).
• USB-PD specs (USB-IF) are free PDFs but huge; for hobby use rely on tester decode rather than reading the spec.
• Watch the rated current — many cheap testers limit to 5 A; PD 3.1 EPR (28 V / 48 V) needs newer testers (KM003C, FNB58) and proper E-marker cables.

Pick this if…

• First USB tester, 2026: FNIRSI FNB48S or FNB58.
• Serious USB-C / PD debug: ChargerLAB POWER-Z KM003C.
• Tinkerer favorite: AVHzY CT-3.
• Pro PD compliance: Total Phase USB-PD Analyzer.
• Use a USB-C charger as a bench rail: PD Buddy Sink (open) or ZY12PDN (cheap).
• One-cable check before a customer ships you USB-C grief: any of the above; they'll all answer the question.